Correct Dip Switch Settings VDO Tachometer

Traveling Writer

I couldn't figure out how to edit an older post's title, so I made a new one for the next poor sap who has to rely on VDO's instructions...

THESE INSTRUCTIONS ARE WRONG

Image may have been reduced in size. Click image to view fullscreen.

For a 4-cyl VW, do just the opposite: 123, UP DOWN DOWN (OFF ON ON)
Beware the dip switches seem to be installed upside down, too. So turn the tach upside down so the numbers read properly before setting!

Using a #1N4007 diode (not #1N4005, tho that might work, too) makes the needle as steady as a rock. Diode in line from negative terminal of coil to tach; white line on diode goes toward the tach.

Cheers!
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Cheers,
Davi

1977 2.0 FI Westy
2011 1200cc Yamaha Super Tenere
1976 Feet (they work surprisingly well)

telford dorr

ScottK · Posted: Wed Apr 22, 2009 2:48 pm Post subject:

Yes, the line on a diode is the cathode end.

Jody '71 · Posted: Wed Apr 22, 2009 3:06 pm Post subject:

Thank you, Thank you, Thank you. So, the instructions they are supplying now are still wrong????? Rolling Eyes

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'66 Beetle
2011 Hyundai Elantra Touring

Cptn. Calzone · Posted: Wed Apr 22, 2009 3:12 pm Post subject: VDO Gauge Tach

I called them (VDO)yesterday and recieved the correct info, and indeed my tach was set up per the old wrong information.
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67 912 Porsche Quintilla
67 Single Cab aka my work horse

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SteveStevieStevens · Posted: Sat May 23, 2009 11:11 am Post subject:

So the picture from VDO above is confusing me. UP/DOWN is all relative to how you're holding the guage, and the ON/OFF is wrong anyway. I believe the switches should look like this:

Since the DIP switches are installed upside down I'm using the printed data on the switch itself. This way switches are:
1 = OFF
2 = ON
3 = ON
When using the ON orientation printed on the black DIP switch itself.

Is that correct?

Krautski · Posted: Sat May 23, 2009 11:37 am Post subject:

I wired and set mine up as per their instructions and it worked. Question

Is everyone else not getting any function at all, or just a bouncy needle?
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SteveStevieStevens · Posted: Tue Jul 21, 2009 8:10 am Post subject:

telford dorr · Posted: Tue Jul 21, 2009 9:13 am Post subject:

As I mentioned in the other thread, VDO seems to be using two different types of switches: one has 'on' in the up position, the other has 'on' in the down position. So if your tach isn't responding correctly, the quick fix method is to flip all switches to their opposite position.

No points to VDO for this mix-n-match parts screw-up - pick a switch supplier and stick with them!
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'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
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SteveStevieStevens · Posted: Wed Jul 29, 2009 7:18 am Post subject:

Flipping the switches did the trick. The Tach wasn't reading over 200 RPM, I switched all the switches to the opposite position and now it's almost dead on with my Dwell/Tach meter. Needle is rock steady without the diode fix too.

Chazbot · Posted: Sat Apr 10, 2010 3:12 pm Post subject:

I'm also having a problem with my recent tach purchase and the switches. I triple checked the instructions and tried both configurations just to be safe. one up and two down, one down and two up.

In one position it reads between 200 and 1200 rpms and in the other it shows me 1200 to 7000. I have my hand held tach hooked up and estimate I'm about 40% over the actual RPMs. The thing is that the calibration dial does not have enough adjustment to compenstate.

The needle is not rock steady. There is some fluxuation. But I'm not sure a diode will take care of it. Does a diode lower the readings to some degree? That might explain the lack of accuracy. Any input would be welcome.

SGKent · Posted: Sat Apr 10, 2010 6:14 pm Post subject:

consider putting the diode in the back off the coll. That way you won't get any bounce out of the line that might confuse a ECU if FI or an electronic ignition. The diode stops the signal from bouncing back and forth.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

Chazbot · Posted: Mon May 17, 2010 8:55 am Post subject:

Just some closure on this one folks. I did get the diode installed and was quite surprised with the change and stability of the tach. I would not have called the needle "bouncing" rather it simply read about twice the normal rpms but was clearly unsteady. It would be nice to get an scope reading on that signal before and after.

Looks like it is working properly now. I may need to make an adjustment still but the needle is stable and I'm pretty happy with it overall.

I'm running a single port 1600 and it appears to be at 3000 rpms at 68 mph.

I ran extra wires to the back in a newly created harness with braided protection. Looking forward to temp and pressure gauges next.

Thanks for all the feedback and support folks! You are all the best...

SGKent · Posted: Mon May 17, 2010 9:00 am Post subject:

I think that the signal from the coil is bouncing back and forth in the wire because of the long distance and that is throwing the tach off. The diode only lets the pulse travel in one direction and stops the bouncing back and forth.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

BumbleBus · Posted: Sat Jul 09, 2011 11:00 am Post subject:

My dwell/tach analyzer ~800rpm idle is reading ~2200rpm on my freshly installed VDO tach. Time to start monkeying around to find the right dip switch settings. I had them like listed above in this thread, but that's not working. If I had hair I'd be pulling it out. Confused

I'm just glad the damn gauge is reading anything at this point. Cool

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'72 L11H Campmobile in various stages of disrepair. Just bumbling along...

SGKent · Posted: Sat Jul 09, 2011 1:43 pm Post subject:

BumbleBus · Posted: Sat Jul 09, 2011 1:53 pm Post subject:

BumbleBus · Posted: Sat Jul 09, 2011 3:50 pm Post subject:

Radio Shack didn't have the 1N4007, but I got a 1N4005, which worked a peach and the needle is smooth now. If you do the exact opposite dip switch for 4 cylinder that's in the VDO guide it works.. for me at least. Sheesh. I still think it's reading a couple hundo fast, but my el crapo tach analyzer may have a weak battery or something also.

Nice to have a tach.
_________________
'72 L11H Campmobile in various stages of disrepair. Just bumbling along...

Vince Waldon · Posted: Sat Jul 09, 2011 6:14 pm Post subject:

In case Search ever leads someone here in the future... anything in the 1N4XXX diode series (1N4001 to 1N4007) should work just fine. They only differ in allowable peak reverse voltage, starting at 50V and going up to 1000V.

http://www.diodes.com/datasheets/ds28002.pdf

Having said that, there can be some funky voltages going on at the coil as the condenser ages, so when in doubt get the biggest numbered diode, if given a choice.


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Correct Dip Switch Settings VDO Tachometer
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