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Tue Mar 04, 2008 4:22 pm

Can someone please help me understand this wiring diagram that I found on the Samba? Thanks to whomever posted the diagram....

I understand the need for the relay; to cut power to the pump in the event the engine dies.

I understand the need (desireability) of the push button over-ride switch; to be able to fill the carb bowl(s) without starting the engine.

What is confusing me is the use of the gen/alt light to trip the relay. I would have thought you would use the oil pressure light. I'm presuming that the pump should be fed power through the relay when the gen/alt light is off (engine running). But, looking at the wiring diagram, it looks like the other way around....that the pump relay would get power when the light is on. What am I not getting, here?

Also, one more thing. What happens if the push button switch is pressed (feeding 12 volts directly to the pump) when the pump is already getting 12 volts supplied through the relay (while engine is running)? Not the normal situation, but it could happen by accident, right?

I'm notoriously bad at posting pictures....but here goes....

Tue Mar 04, 2008 5:58 pm

Having looked at this a little longer....

Maybe what I'm not understanding is how the alt/gen light circuit works. Any experts out there?

Tue Mar 04, 2008 7:25 pm

looks like this diagram was from Speedy Jim's site. Did a search on ramva here is what I came up with:

Quote: Best to put the elec pump up front under the tank.
That eliminates any cahnces of vapor lock.
Put a filter ahead of it.
I agree, bypass the mech pump although you could
leave it in place.

I have a circuit for the elec pump here:
http://www.nls.net/mp/volks/schem/pump.gif
This circuit provides some safety in that the pump
will stop if the engine stalls.
The push button lets you operate the pump after
running the tank dry, for example.

Speedy Jim
http://www.nls.net/mp/volks/

gen light circuit is to turn off fuel pump when engine stalls. Alternator is not spinning => powers up idiot light and relay which in return cuts power to the pump.

Anton

Tue Mar 04, 2008 7:27 pm

Use a Rabbit FI relay. It powers the pump when you're cranking the engine and shuts the pump off when the engine stops. No need for a push button.

Wed Mar 05, 2008 3:50 pm

Anton,

That's what I thought it should do....but the diagram doesn't look that way to me. The relay has to be powered up to get power to the pump. Powering up the relay means the idiot light would be lit. Something seems backwards to me. Take another look at the diagram and see if you see it like I do, or whether I'm completely out of it....

Glenn,

Thanks for the info! I'll have to study it a bit to see if I can understand that one any better than the first one. :oops: I wonder if you can wire in a push button like in the first example....

Wed Mar 05, 2008 4:09 pm

mailman wrote: Anton,

That's what I thought it should do....but the diagram doesn't look that way to me. The relay has to be powered up to get power to the pump. Powering up the relay means the idiot light would be lit. Something seems backwards to me. Take another look at the diagram and see if you see it like I do, or whether I'm completely out of it....

It's confusing, but when the idiot light is on, that wire from D+ is actually a ground, and when the idiot light is off, it is +.

The idiot light works weird. The main source of power for the idiot light comes from the fuseblock. This power goes to the tab at the bottom of the speedo and actually gives power to the oil, gen, and blinker lights. When your car is running and the gen is putting out power, the D+ is giving power to the tab on the actual bulb of the gen idiot light. Therefore the idiot light is getting two positives and no ground. Therefore the idiot light won't come on if the gen is working correctly. When the gen goes bad, the D+ quits giving out power and acts as a ground. This ground combined with the + from the fuse block makes the light go on.

So the relay will only "power up" when the gen is working correctly and D+ is giving out +, which inturn keeps the idiot light off.

Wed Mar 05, 2008 7:15 pm

fluxcap,

That makes sense, and I do believe I understand it now, but I can guarantee you I never would have been able to figure that one out on my own!!! :shock:

Thanks for the excellent description of how it works!

Now one more question....if the relay is powered up, and the fuel pump is operating as it should, what happens if the push-button accidentally gets pushed adding another 12 volt power supply to the mix? Does the pump know the difference? Is this a potential problem?

Wed Mar 05, 2008 7:26 pm

Glenn,

About the Rabbit FI relay....

You said "it powers the pump when you're cranking the engine, and shuts the pump off when the engine stops". That sounds good, but I don't see why you say you don't need the push button.

As I see it, the push button is a manual over-ride to this relay-induced fail-safe circuit. The push button would allow one to power the pump without cranking the engine. This would be great for re-filling the carb bowl(s) after carb repairs or after an extended period of storage. This would greatly reduce the engine cranking required for start-up in those situations.

As for powering the pump during cranking....wouldn't most starting situations be with a carb(s) with full float bowls? All except the situations I've already mentioned, and they're covered by the push button....

Wed Mar 05, 2008 7:30 pm

One more question guys, while I'm on a roll... :wink:

Why wouldn't one use the oil pressure idiot light instead of the alt/gen light? It seems to me that the circuit is simpler, just a simple pressure switch, and would accomplish the same thing.

Would it work as well?

Wed Mar 05, 2008 7:34 pm

The oil light is a ground switch.

By using the Rabbit relay the pump will work when the engine is being cranked and running. The pump will shut off when the engine stops.

So if you're ever in a accident and the fuel line bursts, the pump won't continue running and be a fire hazard.

Wed Mar 05, 2008 7:34 pm

mailman wrote: One more question guys, while I'm on a roll... :wink:

Why wouldn't one use the oil pressure idiot light instead of the alt/gen light? It seems to me that the circuit is simpler, just a simple pressure switch, and would accomplish the same thing.

Would it work as well?

I am guessing different safety, let's say you throw a belt, pump will be disabled. But schematics will be different because of how D+ functions...

Anton

Wed Mar 05, 2008 7:41 pm

Glenn,

I hear what you're saying, but I guess I'm missing something (again!).

In the wiring diagram I posted, using the relay and the push button, the fuel pump also stops if the engine stops running. Same protection against fuel line breakage in a crash, right? (I hate to sound stupid, here, but I just want to be sure I understand this. Thanks for bearing with me...)

Anton,

I see what you mean about the thrown belt.....

Wed Mar 05, 2008 7:44 pm

mailman wrote: Glenn,

I hear what you're saying, but I guess I'm missing something (again!).

In the wiring diagram I posted, using the relay and the push button, the fuel pump also stops if the engine stops running. Same protection against fuel line breakage in a crash, right? (I hate to sound stupid, here, but I just want to be sure I understand this. Thanks for bearing with me...)

Anton,

I see what you mean about the thrown belt.....
Agreed... but you don't need a push button to get the engine started. The relay powered the pump when the engine cranks.

Thu Mar 06, 2008 5:20 am

Glenn,

I guess I'm just used to mechanical pumps. Since I store my car all winter, the carb bowls (and perhaps the fuel pump) evaporate completely dry. Come spring, it requires quite a bit of cranking to fuel those carbs again before the engine will start. Having the ability to run the pump without cranking the engine just seems like a good plan.

Maybe the electric pumps push enough additional volume that the carbs would fill faster as the engine cranks...I don't know. But for the negligable additional cost of a simple push button switch, I thought I'd like to have that option. :wink:

Thu Mar 05, 2009 4:00 am

Glenn wrote: Use a Rabbit FI relay. It powers the pump when you're cranking the engine and shuts the pump off when the engine stops. No need for a push button.

just to let you all know..there is pretty neat relay of this partnumber for sale on E*bay, new, with integrated slot for a fuse.

Where do I add a manual override button to this relay circuit? I want to be able to prime my carbs before I start cranking the engine. Between 15 and 87 or between 30 and 87?

Wed Mar 24, 2010 2:05 am

1961bluebug wrote: Glenn wrote: Use a Rabbit FI relay. It powers the pump when you're cranking the engine and shuts the pump off when the engine stops. No need for a push button.

just to let you all know..there is pretty neat relay of this partnumber for sale on E*bay, new, with integrated slot for a fuse.

Where do I add a manual override button to this relay circuit? I want to be able to prime my carbs before I start cranking the engine. Between 15 and 87 or between 30 and 87?

I don't understand what you mean: Trigger to coil #1 points... Where do I put this wire? Sorry I am ignorant...

Fri Apr 01, 2011 1:56 pm

Glenn wrote: Use a Rabbit FI relay. It powers the pump when you're cranking the engine and shuts the pump off when the engine stops. No need for a push button.

Any good suggestions for mounting this relay? Just put in an electric pump and used this relay, but it's just a box with no mounting tab. I guess it's initial application was to be plugged into a box.

Right now it's fastened to the ashtray box with some ghetto zipties :lol: , and I don't plan on leaving it like that very long. Just want to make sure it gets secured since terminal 30 is always hot (i do have it fused though).

If anyone is using this relay, I'm curious to how you mounted it.
Thanks!!!

Sun May 22, 2011 4:10 pm

I beleve German Supply sells a socket for it :wink:

Sun May 22, 2011 5:31 pm

Thanks, I did eventually find that a few places sold the socket. Unfortunately, the relay I got (from ebay) ended up being a dud. It would not cut off when I stalled the car. I could hear it clicking as if it were trying to cut off, but it would just keep on running.

Ended up getting one of these http://revolutionelectronics.com/Fuel_Pump.html and have been super happy with it.

Sun May 22, 2011 6:09 pm

fluxcap wrote:

Ended up getting one of these http://revolutionelectronics.com/Fuel_Pump.html and have been super happy with it.
I got one of those also and so far it's been working great.