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Double relay/alternate use?
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shaunone
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PostPosted: Sat Aug 27, 2011 8:11 am    Post subject: Double relay/alternate use? Reply with quote

I have a 77 camper with 74 1.8 that has been converted to a weber progressive, (mine finally runs good so don't try to convert me now!) Anyways, I've been meaning to hook up a fuel pump relay for safety reasons to my electric fuel pump. My firewall looks like this, except it is missing both white harness'/plugs on the right.

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

I only have the one plug connected on the left. First of all, what does this hooked up one do? Also, can I use what looks like a relay (the middle empty plug) to switch my fuel pump? What about the far right plug? I no longer have the booster fan either...Can I hook up a OG booster fan with a single weber setup? Is it worth it? Additional cooling? Sorry for the many questions, any help is greatly appreciated.
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Tom Powell wrote:
Olddog52 wrote:
one tab to ground, the other to a 12 volt source. Listen intently for a sound.


I put the horn next to my ear and I could hear the ocean.
When I hooked up the battery I couldn't hear anything for three days.



Last edited by shaunone on Sat Aug 27, 2011 3:07 pm; edited 1 time in total
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shaunone
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PostPosted: Sat Aug 27, 2011 10:38 am    Post subject: Reply with quote

bump
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Tom Powell wrote:
Olddog52 wrote:
one tab to ground, the other to a 12 volt source. Listen intently for a sound.


I put the horn next to my ear and I could hear the ocean.
When I hooked up the battery I couldn't hear anything for three days.

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SGKent Premium Member
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PostPosted: Sat Aug 27, 2011 10:43 am    Post subject: Reply with quote

Are you just looking for something to do or trying to solve an issue, and if so what is it?
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Randy in Maine
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PostPosted: Sat Aug 27, 2011 10:59 am    Post subject: Reply with quote

The top one is the "series resister" and the bottom one is the double relay.

Give them to someone with a FI set up for spares.[/youtube]
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shaunone
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PostPosted: Sat Aug 27, 2011 11:31 am    Post subject: Reply with quote

Sorry guys, maybe I should've been a little more clear. I want to install a safety relay for my electric fuel pump. Right now the pump is hardwired to the coil. I was going to buy a generic relay at the FLAPS for this purpose. Then I noticed this empty relay in my engine compartment. Can I use this relay for the same purpose? It looks like a double relay, and the other is being used. What is the other side being used for? Can I use the empty side without affecting the side that is hooked up?
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Tom Powell wrote:
Olddog52 wrote:
one tab to ground, the other to a 12 volt source. Listen intently for a sound.


I put the horn next to my ear and I could hear the ocean.
When I hooked up the battery I couldn't hear anything for three days.

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shaunone
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PostPosted: Sat Aug 27, 2011 3:49 pm    Post subject: Reply with quote

I guess I'll just buy a cheap relay from CT and forget about this whole double relay thing...
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Tom Powell wrote:
Olddog52 wrote:
one tab to ground, the other to a 12 volt source. Listen intently for a sound.


I put the horn next to my ear and I could hear the ocean.
When I hooked up the battery I couldn't hear anything for three days.

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SGKent Premium Member
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PostPosted: Sat Aug 27, 2011 4:12 pm    Post subject: Reply with quote

shaunone wrote:
I guess I'll just buy a cheap relay from CT and forget about this whole double relay thing...


It would be easier. What you want to do could be done but most likely none of us have the time to design and walk you through it. Not only that but you have no guarantee that the reason the FI got pulled off was a bad double relay and the mechanic didn't know how to troubleshoot it so a carb went on. Using a new relay would be a good thing. Now the downside - if the relay sticks the fuel pump will stay on. Might be better to put a real switch under the dash that turns it on and run that through the ignition switch as well. If it is not obvious it becomes a cheap alarm kill too. Let's a thief drive far enough to get away from you and then it dies on him so you are out of danger.
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shaunone
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PostPosted: Sat Aug 27, 2011 4:32 pm    Post subject: Reply with quote

That's interesting, because the only reason I wanted to install one was because everyone on here suggests a relay. But like you say, if the relay sticks you could cause big problems as well. So you are thinking that a guy should install an actual switch AND a relay? That way the relay doesn't stick while you're parked overnight and fill the whole block with gas?
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Tom Powell wrote:
Olddog52 wrote:
one tab to ground, the other to a 12 volt source. Listen intently for a sound.


I put the horn next to my ear and I could hear the ocean.
When I hooked up the battery I couldn't hear anything for three days.

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SGKent Premium Member
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PostPosted: Sat Aug 27, 2011 4:45 pm    Post subject: Reply with quote

shaunone wrote:
That's interesting, because the only reason I wanted to install one was because everyone on here suggests a relay. But like you say, if the relay sticks you could cause big problems as well. So you are thinking that a guy should install an actual switch AND a relay? That way the relay doesn't stick while you're parked overnight and fill the whole block with gas?


Yes - the idea is to get the load off the ignition switch.

You can have the best of all world if you want. Run a line from the accessory position on the ignition to the energizing coil on the relay. Then run a fused "always-on" wire from the fuse box through the relay points through the kill switch then back to the pump. That takes the load off the ignition switch and also gives you a permanent kill when you are out of the bus. It also makes it so if someone hotwires the bus to steal it they only drive as far as the fuel in the bowl will take them.

Relys don't often weld points shut but it does happen. They also fail the other way sometimes and refuse to make contact between the points. I have seen three position switches used where center is off. 1 side is power from the ignition switch thru a relay and the other side is power through the ignition switch without the relay.
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jtauxe
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PostPosted: Sat Aug 27, 2011 9:50 pm    Post subject: Reply with quote

Put the double relay, resistor block, and other old FI parts up in the classifieds so that other FI folks can use them.
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greenbus pilot
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PostPosted: Sat Aug 27, 2011 10:25 pm    Post subject: Reply with quote

Find a FUEL PUMP RELAY from an early Rabbit, etc and use that. It has an additional input from the ignition circuit- if the engine stops, so does the pump. I assume it has a logic circuit in it for 2 inputs. Check a wiring diagram for water cooled cars and follow suit. Thats what I did. It is no more work than using a generic relay and screwing around trying to emulate the real deal. If you can find one in the boneyard you can get the socket also, should be cheap or free, depending on yard personnel, customer attitude, moon phase, etc. Rolling Eyes
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shaunone
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PostPosted: Sun Aug 28, 2011 8:30 am    Post subject: Reply with quote

Thanks guys, off to the junk yard I go!
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Tom Powell wrote:
Olddog52 wrote:
one tab to ground, the other to a 12 volt source. Listen intently for a sound.


I put the horn next to my ear and I could hear the ocean.
When I hooked up the battery I couldn't hear anything for three days.

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Vince Waldon
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PostPosted: Sun Aug 28, 2011 9:29 am    Post subject: Reply with quote

greenbus pilot wrote:
Find a FUEL PUMP RELAY from an early Rabbit, etc and use that. It has an additional input from the ignition circuit- if the engine stops, so does the pump.


This.... which is why reusing the relay that's there is not optimal, nor is a generic relay from Canadian Tire. Wink
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Tcash
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PostPosted: Sun Aug 28, 2011 11:11 am    Post subject: Reply with quote

Hi if I understand you right your primary concern is safety. A relays purpose is to control a large current (your pump) with a small current (your ignition switch). That being said. Your driving along and pow, you get hit. Your rendered unconscious. The engines stopped, but the Ign. key is still on, the fuel pump is pouring fuel onto a already lit fire. You need to wire in a Inertia switch or oil pressure switch . This will shut the pump down in the event of an accident. Good Luck hope this helps.

Last edited by Tcash on Sun Aug 28, 2011 2:07 pm; edited 1 time in total
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telford dorr
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PostPosted: Sun Aug 28, 2011 12:37 pm    Post subject: Reply with quote

Or wire a relay coil from ground to the blue wire going to the alternator / generator regulator. When the generator is putting out power, the relay will activate. You would wire the relay contacts to provide power to the fuel pump. Thus, if the engine stops, so should the fuel pump.

I'd supply a bypass switch in case of generator failure, so you won't be stranded.

Ref: aux blower on late type 4 engine bays uses the same setup.
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PostPosted: Sun Aug 28, 2011 12:56 pm    Post subject: Reply with quote

Tcash wrote:
You need to wire in a Inertia switch or oil pressure sensor . This will shut the pump down in the event of an accident. Good Luck hope this helps.


VW Rabbit fuel pump relay accomplishes the same thing.... it watches the points and if they stop it shuts off the fuel pump for safety.

Lots of different ways to skin this cat. Wink
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Tcash
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PostPosted: Sun Aug 28, 2011 2:05 pm    Post subject: Reply with quote

Tcash wrote:
Hi if I understand you right your primary concern is safety. A relays purpose is to control a large current (your pump) with a small current (your ignition switch). That being said. Your driving along and pow, you get hit. Your rendered unconscious. The engines stopped, but the Ign. key is still on, the fuel pump is pouring fuel onto a already lit fire. You need to wire in a Inertia switch or oil pressure sensor . This will shut the pump down in the event of an accident. Good Luck hope this helps.


I goofed, it is not a Oil Pressure Sensor. Correction Oil Pressure Switch Sorry I will make the correction.
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Tcash
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PostPosted: Sun Aug 28, 2011 2:24 pm    Post subject: Reply with quote

greenbus pilot wrote:
Find a FUEL PUMP RELAY from an early Rabbit, etc and use that. It has an additional input from the ignition circuit- if the engine stops, so does the pump. I assume it has a logic circuit Rolling Eyes


That's neat, would be easier than plumbing in a Oil Press. Switch. I am not familiar with with Rabbits do you remember about what year vehicle they came in?
Thank You
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Tcash
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PostPosted: Sun Aug 28, 2011 2:43 pm    Post subject: ratwell fuel pump relay with connections to coil Reply with quote

Another one from ratwell. Thanks. Link gives part number, wiring directions and circuit schematic for the Audi-Rabbit relay. Good information

http://www.ratwell.com/mirror/sfraser/relay.html
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PostPosted: Sun Aug 28, 2011 3:08 pm    Post subject: Reply with quote

I like that circuit even better than my suggestion above (if you can find the part. Wouldn't even be that hard to build...)
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