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Water level indicator LED always green / sensor troubleshooting
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madspaniard
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PostPosted: Tue May 12, 2009 11:08 pm    Post subject: Reply with quote

singler3360 wrote:
Just received a replacement Fresh Water Tank Level Sensor, plugged it in AND...
the green water level indicator light still stays on. Darn.

The float on the new sensor does not float, sinks like a rock. I don't hear the clicking of the reed switches as the float unit is moved up and down the rod. I've traced wires, connections and fuses and everything else looks good. When the led panel switch is ON, the green wire at the water tank reads 0.3V.

So, is this a tale of two bad in-tank sensors? Should I have the vendor send me a third?


first try borrowing one that you know it works from a fellow westy owner
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singler3360
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PostPosted: Wed May 13, 2009 8:30 am    Post subject: Reply with quote

Thanks Mad.

Anyone in the Corvallis, OR area willing to let me try their sensor for a few minutes? Beverages provided.
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dbeierl
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PostPosted: Wed May 13, 2009 11:24 am    Post subject: ...It's the chip... Reply with quote

singler3360 wrote:
The float on the new sensor does not float, sinks like a rock.


So this is obviously a bad sender no matter what it does electrically.

Quote:
I don't hear the clicking of the reed switches as the float unit is moved up and down the rod. I've traced wires, connections and fuses and everything else looks good. When the led panel switch is ON, the green wire at the water tank reads 0.3V.

So, is this a tale of two bad in-tank sensors? Should I have the vendor send me a third?


Well...you've got a bad float on the new sender but you haven't established yet that the old one is bad. You may end up with a spare sender if they won't refund for the one you just got.

You say you have 0.3v at the green wire -- is that with sender unplugged? If so, then for sure the board has a problem, almost certainly the left-hand chip. With sender unplugged you should see +12 on the green wire (using a digital meter), and no LEDs lit.

The sender (unplugged) should show resistance across its leads of roughly zero with float at bottom, roughly half a meg halfway, roughly a megohm at top.

271-1356 -- five-pack of one-megohm resistors, $0.99. Leads open, no light. One resistor, red light. Two resistors in parallel, yellow light. Leads shorted, green light. If not, again almost surely the chip.

If you really really don't want to solder on the board, send it to me with $30 and I'll take care of it and send it back. But better for your soul to do it yourself if you can. Smile
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dbeierl
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PostPosted: Wed May 13, 2009 11:28 am    Post subject: Reply with quote

madspaniard wrote:
first try borrowing one that you know it works from a fellow westy owner


Those senders are so delicate mechanically that I think it's a poor idea to handle them at all unnecessarily (though I definitely recommend removing them from the tank when washing out the tank). The senders are easily tested with an ohmmeter, and the board with a couple resistors or a pot.
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singler3360
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PostPosted: Wed May 13, 2009 10:18 pm    Post subject: Re: ...It's the chip... Reply with quote

dbeierl wrote:

If you really really don't want to solder on the board, send it to me with $30 and I'll take care of it and send it back. But better for your soul to do it yourself if you can. Smile


dbeierl, thanks very much for the posts as I try to figure this one out. I will try to solder on a new chip but will keep your offer in mind for sure as a backup.

The 0.3V reading was with the sensor unplugged and the probes on the green and black connectors inside the clear plastic protector. I think I'll go for it at this point. Will report back afterward.
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dbeierl
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PostPosted: Wed May 13, 2009 11:05 pm    Post subject: Re: ...It's the chip... Reply with quote

singler3360 wrote:

dbeierl, thanks very much for the posts as I try to figure this one out. I will try to solder on a new chip but will keep your offer in mind for sure as a backup.


Clip the chip off the top of the board with small diagonal cutters. Then you can desolder and pull each individual pin with tweezers; then use desoldering braid to clear solder from the holes before inserting the new chip.

Use thin 60/40 or 63/37 rosin-core solder. 63/37 is a bit more expensive (more tin) but doesn't go through a pasty stage as it solidifies. Don't use 50/50 and don't even think about plumber's flux...

Don't scrub or press the iron on the braid or circuit foils -- the foil is glued onto the board, and the glue is very delicate when hot. If heat isn't transferring properly from the iron, add a drop of solder to the tip. Tip-cleaning sponge, desoldering braid etc all available from Radio Shack.

Clean clean clean -- your soldering tip must always be shiny bright in use. Wipe it on the barely-damp sponge each time you pick it up; when you put it down, add a drop of solder on the tip so it doesn't burn.

To bend the legs of the new chip in, lay it on its side and grip the ends to press the legs in; then turn it over to do the other side. You need firm downward pressure so the increased bend happens at the existing corner -- otherwise they will bend where they get thin, which you don't want. Chips are shipped with legs sprung out so that automatic inserting equipment can get a good grip on them and they'll stay put after insertion.

Show your board to a local TV shop -- see if they have a similar junk board you can practice on. Make sure they give you a single-sided board as double-sided ones are much harder to work on.
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singler3360
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PostPosted: Mon May 18, 2009 8:30 pm    Post subject: Reply with quote

I could get another chip ($1.69 at RS) and try again? READ ON:

Thanks to dbeierl's advice, I got the chip, desoldered the old one off (without having to clip it off) and got the new one soldered on. Installed it, flicked on the switch and it actually went from the stuck green light to amber. The tank is less than half full, so I'm thinking AWESOME. I decided to see if when I pulled the sensor and the float went to the bottom if the red light would come on. Instead, I got smoke from the board and now the green and amber lights are stuck on. I'm thinking when I soldered the new chip I got solder between the individual legs/contacts and it shorted out. Could this be the reason for the sizzle and smoke?

Also, I've asked BusDepot for an RMA to return the sensor they sent me that has the float that sinks regardless of water level. After an initial response to tell me they didn't think it was the sensor unit, they are now not returning my inquiries. Anyone else have this problem with them?

What a hassle!
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dbeierl
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PostPosted: Mon May 18, 2009 8:53 pm    Post subject: Reply with quote

Bummer...

singler3360 wrote:
I'm thinking when I soldered the new chip I got solder between the individual legs/contacts and it shorted out. Could this be the reason for the sizzle and smoke?


Could be -- if so you have to do better next time. Soldering pins together is a good way to let the magic smoke out. Check carefully before you put power on the board. It's also conceivable that you got a bad chip from RS. If the next one smokes <you did put it in right way around, yes? They both face the same way> then obviously there's more going on than meets the eye and maybe it's time to send it out.
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singler3360
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PostPosted: Tue May 19, 2009 10:37 pm    Post subject: Reply with quote

Bought another IC chip today and this time carefully soldered it on, making sure each soldering point did not short with the one next to it. Works great now just like it should. It turns out there was nothing wrong with the water level sensor unit, so it remains.

PM'ed the BusDepot customer service rep who had posted elsewhere in Samba and by 10am this morning I had a phone call to resolve, to my satisfaction, the faulty replacement sensor they had sent.

All in all, could not have done this without help here. Thanks to all.
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dbeierl
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PostPosted: Tue May 19, 2009 10:43 pm    Post subject: Reply with quote

Congrats!

Smile
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PostPosted: Sat Jul 19, 2014 9:45 am    Post subject: Thread Revival... Reply with quote

Working on a 87 GL camper...

We have the metal lug sensors imbedded in the side of the tank.

The indicator panel works for battery voltage but not for water level. The green output wire to the sensors only shows a fraction of a volt, so it looks like we need to replace the left hand chip. Any ideas as to why that would fail? Age? The PO had franken-wired things, so maybe he fried it?

Also I tested the black resistor(?) pack that hooks up to the top three lugs. With 12 volts (from a PS, not from the indicator panel) applied to the top green wire I would have expected *something* like 8V and 4V at the outputs to the lower lugs, but I only see a fraction of a volt. Anybody know what that resistor pack is *supposed to produce?

If that's toast too, can you just take it apart and replace the resistors, or is it a more complicated IC? I haven't pried it apart yet.

Anybody know of a diagram for this system, with appropriate outputs volts and resistances?
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kalispell365
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PostPosted: Sat Jul 19, 2014 5:04 pm    Post subject: Reply with quote

You can test the input with a potentiometer and voltmeter. Input lead is biased to B+ with one megohm, electrodes ground out successive resistors in a voltage divider inside the little black module by the tank. Result compared against similar network at the left-side LM324 chip.

First unplug the green wire at the tank. You can plug and unplug freely with panel power on. None of the tank LEDs should be lit. Then ground the green wire. The green LED only should light. If either of these tests fail, skip immediately to the second section, called LM324s die a lot. Return to this section for info later. Otherwise continue from here:

To test the thresholds connect a digital voltmeter from the green wire to ground and either:

    A) Operate the sender float on newer ones (be *very* cautious; if you bend the rod the tiniest bit in the wrong direction it will break one or both reed switches inside because no slack was left when soldering them). The meter will pull the voltages down somewhat, see NOTE 1 below and method/formula at C).

    B) Ground all the sender terminals on the older tanks to the bottom terminal and then remove them beginning from the top, same comments about meter as above. The tank should be empty. If you want to keep water in the tank you can disconnect the electrode wires and short them together in the right order, but mark them carefully before you disconnect them.

    C) Disconnect the green lead and connect to ground via one end and middle of a 10-20 megohm pot, preferably linear taper, and adjust the pot. With this method you can find the actual thresholds. A ten megohm pot and a ten megohm meter will give you about 10.5V maximum which is plenty. If you want to know what the actual applied resistance is at each threshold, unhook the green lead, switch the meter to ohms, write down the value and calculate Reffective = Rmeter x Rpot / (Rmeter + Rpot). Same method if you want to know how the meter is altering sender resistances in previous methods.

    D) Disconnect green lead and connect positive side of a variable power supply to it, negative side to ground.

    CAUTION: do not apply power with the panel turned off (if the panel power switch is pulling out of the solder, fix that first to avoid possibly losing panel power while your supply is driving the line).

    CAUTION: Do not exceed the measured voltage present on the green wire with panel on and nothing connected, and do not allow the voltage to go negative more than a few millivolts. Some variable supplies may go slightly negative when set to minimum, so check and beware. The chip can handle a very slight negative input; that's how the flame detector LED operates, the fridge thermocouple is the only voltage in the van that's officially negative to chassis ground. But the emphasis is on very slight.

    E) Connect various combinations of dry cells likewise. See CAUTION above.

    F) Connect individual resistors likewise ranging down from ten megohms. This is the hard way for sure, but if you have a bunch of resistors it works.


NOTE 1: With either method where you're actually supplying voltage, adding about 5,000 ohms in series will prevent any excitement resulting from shorting a wire to ground. The green wire itself can be grounded safely.

NOTE 2: If you're not actively supplying voltage you will get most useful results with a ten megohm (or higher) voltmeter. Most digital meters have ten megohm sensitivity on voltage ranges, but some cheap ones may be one megohm. A ten megohm meter will drag the green wire down to about 11.5V all by itself, and a one megohm meter will drag it to about 6.3V, severely limiting your testing.

Assuming the LED panel is being fed by 12.6V, the following voltages at the end of the green wire should have the following results with a few per cent variation for differing resistor errors on the LED board (if all resistors were x% off in the same direction the thresholds would not change):

12.6-9.45 -- No lights (no bolt jumper/not reachable with float sender. Signals </= one liter in the tank)
9.45-7.35 -- Red (bottom sender bolt jumpered to next up/float sender at bottom)
7.35-5.25 -- Yellow (add jumper to next bolt/float sender at middle)
5.25-0.00 -- Green (add jumper to top bolt/float sender at top)

OOPS: Exact values of above numbers are suspect, I'll have to recheck the spreadsheet.

Note that varying battery voltage will change the voltage thresholds proportionately; but will not cause them to shift relative to the operation of a particular sender. The circuit employs three of the four amplifiers contained in the left-hand chip on the panel(the fourth one is a spare). Each amplifier drives one LED, and independently drives that LED any time the output of the voltage divider formed by the various discrete resistances of the sender in series with one million ohms becomes even microscopically less than the output of a particular tap on a reference voltage divider (made up of five resistors on the panel).*** Since both the sender-side and reference-side networks are powered by the same battery voltage, the ratio between them does not change.

***Ordinarily that would mean that the lights would show red, yellow+red, green+yellow+red; but the LEDs are wired in trick fashion so the red one loses its ground when the yellow comes on, and the yellow loses its ground when the green comes on. This is done simply by using the connecting LED- of the red and yellow LEDs to the adjacent LED+ instead of ground. The amplifiers can hold the line either high or low (to say another way they can either source or sink current) so they can easily act as the "ground" for an LED.

Incidentally, a different arrangement is used for the battery meter, because there you *want* the result to change when battery voltage does. There a very similar ladder of resistors becomes the sensing part of the arrangement; and the (resistor + changing resistor) pair used for the tank sender becomes instead a (resistor + zener diode) pair which changes output voltage very little with any reasonable change in battery voltage. As with the water side, lighting one LED removes the ground from the previous one.

If you were to add the 500k resistor I refer to in my schematic, the thresholds would change thus:
12.6-9.72 -- No Lights
9.72-7.56 -- Red
7.56-5.4 -- Yellow
5.4-0.00 -- Green

OOPS: Exact values of above numbers are suspect, I'll have to recheck the spreadsheet.

I made this change on my '84 to prevent the panel indicating red when it should have been showing yellow. Adding that single resistor changed all the thresholds because it altered the overall value of the string; to manipulate one threshold without altering the others could be done in various ways. The simplest would be to leave the original resistor string alone and simply re-route the input to that amplifier to a separate pair of resistors having the correct ratio. If the designers had envisioned a need to adjust the thresholds they would have used a separate divider for each amplifier, probably with a tweak adjustment included. It all costs money though, and board real estate.

The LM324 chips die a lot, at least on this board. Seriously.

If the battery lights work OK but the water tank lights don't all go out when you unhook the green wire and the green (only) doesn't light when you ground it (or if the battery lights start to misbehave), your first action is to replace the left-hand LM324N with another LM324; because it's highly likely that the chip If Radio Shack still carries them that's fine, otherwise get one or a few from wherever. Chip price used to be in the dollar range; I haven't looked for a few years. If you aren't up to soldering (and this is about as easy a board to work on as exists, see below for method) get whoever does the job for you to install a socket on both sides instead, so you can easily change or swap them yourself later.

Unfortunately, I just took a look at my photo of the board and there may be no room to put sockets in. What could be done is to add individual socket terminals through the board after enlarging the holes slightly. They would sit practically flush on top and wouldn't raise the chips much at all. However I can't really tell from the angle, and a low-profile socket might do fine. The controlling depth is the plane of the top of the switch body and the shoulders of the LED ends as they are what seats up against the rear of the metal panel. If someone measures that clearance depth I can get a better handle on this. Back to business:

The three troubles that afflict this setup (no special order):

    1) Learning the hard way that the float-type sender as originally built (and I hope and believe that Trevor has arranged for some slack in the assembly of the new ones) is ABSOLUTELY INTOLERANT of being bent the slightest amount in the direction away from the foil side of the circuit board inside, where the reed switches are soldered on. One or both of the glass reed switches will burst because their leads will separate and glass doesn't stretch much. Repairing is often practical and once you're inside you can put some slack in the soldered leads so it won't happen again. Best way I found to open them was with a plumbing-type tubing cutter used very carefully and rejoined with a rigid oversleeve. **One of the reed switches is a simple N/O type with two terminals and is easily sourced. The other has three terminals and is a bit harder to locate. This circuit carries extremely low current so if a lighter/smaller switch presents itself it will be fine so long as the magnet in the float can operate it and you're even more careful to put slack in the leads. Larger ones the same except they also have fit into the tube which may not accept anything larger. Note which way the three-terminal switch is oriented since the N/O and N/C terminals must be correct. Test the board with the LED panel or ohmmeter and a magnet before assembling. The resistance changes should be in consistent order up and down as you move the magnet. I can't remember exactly how it's wired right now so I'm going to wave my hands vaguely. Anyone with a good float sender can provide correct ohmmeter readings.

    1a) Getting a drop or two of water inside said float sender, either from a leaky joint or more likely through the top where the wires come out. This causes troubles where the tank reads too high, but the reading is likely to shift as the panel stays on for a while. This can be repaired by drilling a small hole next to the bottom, breaching the seal around the wires if need be, and flushing through several changes of 190 Everclear or Denatured Alcohol or high-strength isopropyl alcohol dried with air or vacuum between changes ; then over-cementing assembly seams as well as closing the hole you made and the top seal.** But don't be surprised if you break a switch in the process -- so really it's better to ever so gingerly open it up as above and re-solder one of the leads of each reed switch so the board can flex a bit without popping them. Check for corrosion/electrolysis eating up the copper and clean and solder over it if need be. Then dry out the tube and circuit board and put everything back together. And triple-protect the entry point at the top as I think that's where the water usually gets in. I personally would advise removing the wand from the tank and storing it safely before any sort of cleaning activity inside or outside the tank for both flexing and leakage reasons.

    1c) Having to scrub off the older-type tank electrodes with green Scotch-Brite, not the wussy blue stuff. Maybe adding a few inches of salt to a tank if the water's really pure.

    ** I'm sorry, you'll have to experiment or do some research for a cement that will bond properly. Cheri or Trevor can no doubt supply that info now; they weren't involved with the senders when I was fixing them.

    2) Power switch working loose from the solder. It's a very small switch supported only by its leads and it has a hard life from bumping, vibration, something. I used to routinely re-solder mine any time I had the panel out.

    3) LM324 gone bad for no obvious reason.


That's it. I have never heard of any other difficulty with them ever.

OK, I will check the threshold exact numbers and take another pass through probably tomorrow some time. If you (anyone) notice any problems in the meantime let me know. I'm a bit sideways on sleep this past week and my proofreading has suffered.

Some info and schematics here: http://pws.prserv.net/synergy/Vanagon/LEDpanel.htm

NOTE: NOT mine, saved from another forum. Hope this helps. Very Happy
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Last edited by kalispell365 on Mon Jul 21, 2014 4:37 pm; edited 1 time in total
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merlinj79
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PostPosted: Sat Jul 19, 2014 10:26 pm    Post subject: Reply with quote

Thanks man, that's awesome.

The good news is that the whole assembly is out of the van, so I hooked it all up on the bench using meter probes in a glass of water for electrodes (we have the old style tank) and it works fine.

I'll clean the tank electrodes tomorrow and try again...
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PostPosted: Mon Jul 21, 2014 3:48 pm    Post subject: Reply with quote

merlinj79 wrote:
Thanks man, that's awesome.

From the author of the piece, you're welcome. Smile
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PostPosted: Mon Jul 21, 2014 4:36 pm    Post subject: Reply with quote

dbeierl wrote:
merlinj79 wrote:
Thanks man, that's awesome.

From the author of the piece, you're welcome. Smile


I hope I didn't offend you, I saved your writing for myself and found it MOST useful. I just couldn't remember where I got it from specifically. What an incredible write up.

I also want to thank you so much!
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PostPosted: Mon Jul 21, 2014 4:39 pm    Post subject: Reply with quote

kalispell365 wrote:
dbeierl wrote:
merlinj79 wrote:
Thanks man, that's awesome.

From the author of the piece, you're welcome. Smile


I hope I didn't offend you, I saved your writing for myself and found it MOST useful. I just couldn't remember where I got it from specifically. What an incredible write up.

I also want to thank you so much!

Not a problem, mate. It's on the Vanagon list, and I hope before long to re-do the calculations for the threshold voltages. I think most of the other errors were cleaned up by that version.

Smile
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PostPosted: Sat Sep 15, 2018 12:03 pm    Post subject: Re: water level indicator led always green Reply with quote

I had the LED light always green issue. Iíve read all that is here and have replaced the lower (normally closed) reed switch from an old sender unit I had that I determined to be working by running a magnet over it.

When I tested it hooked up in the van, it seems to work, as the float magnet passes the reed switches except for example when the float goes up past the top reed switch the LED goals from yellow to green and then back to yellow as the float/magnet stops at the stopper. There is a similar scenario at the bottom switch with lights going from yellow to red and back to yellow. I did manage to get the lower float stopper off the tube and I think I have it back in the same place based on the glue marks but...

My question is in order for the lights to stay green and red at the top and bottom extremes of float travel, does the float/magnet have to be stopped over top of the reed switch. In other words if the float goes past the reed switch too far does the switch revert and the light change? Also does it matter which way the float/ magnet is on the tube, ie. is the magnet at one end of the float and so itís orientation affects weather the reed switch says in the magnetic field when the float has hit the stopper?
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PostPosted: Sat Sep 15, 2018 12:36 pm    Post subject: Re: water level indicator led always green Reply with quote

I looked up how that works once but I've since forgotten. I think there are 2 switches for the 3 color choices. If the bottom switch is closed you get a red. As soon as it leaves the bottom switch, it goes yellow as default. Then it if closes the top switch it goes to green. Something like that IIRC.
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PostPosted: Sat Sep 15, 2018 2:49 pm    Post subject: Re: water level indicator led always green Reply with quote

coastdog wrote:

My question is in order for the lights to stay green and red at the top and bottom extremes of float travel, does the float/magnet have to be stopped over top of the reed switch. In other words if the float goes past the reed switch too far does the switch revert and the light change?

Yes.

Quote:
Also does it matter which way the float/ magnet is on the tube, ie. is the magnet at one end of the float and so itís orientation affects weather the reed switch says in the magnetic field when the float has hit the stopper?

No.
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PostPosted: Sat Sep 15, 2018 2:54 pm    Post subject: Re: water level indicator led always green Reply with quote

davevickery wrote:
I looked up how that works once but I've since forgotten. I think there are 2 switches for the 3 color choices. If the bottom switch is closed you get a red. As soon as it leaves the bottom switch, it goes yellow as default. Then it if closes the top switch it goes to green. Something like that IIRC.

One reed switch (bottom IIRC) is an SPDT switch. The other is the more common SPST type.

I've had a number of these apart to repair them after either water intrusion (a few drops past the wire entry at top is enough to bother them) or reed switch breakage due to bending the wand -- the original production had zero slack in the reed switch leads, so the tiniest bend in the wrong direction would pop one or both. I had a long discussion about this with Trevor (The Skylight Guy) when he started up production again and I hope and believe that the current ones are assembled more thoughtfully.
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