Proper electric fuel pump wiring

[mailman]

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....

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'64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop)

[mailman]

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?
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'64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop)

[akokarski]

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

[Glenn]

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.

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Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"

Member #1009

#BlueSquare

[mailman]

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. I wonder if you can wire in a push button like in the first example....
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'64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop)

[fluxcap]

[mailman]

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!!!

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?
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'64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop)

[mailman]

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....
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'64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop)

[mailman]

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

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?
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'64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop)

[Glenn]

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.
_________________
Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
"You may not get what you pay for, but you always pay for what you get"

Member #1009

#BlueSquare

[akokarski]

[mailman]

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.....
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'64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop)

[Glenn]

[mailman]

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.
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'64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop)

[1961bluebug]

[[email protected]]

[fluxcap]

[canvmnvw]

I beleve German Supply sells a socket for it

[fluxcap]

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.
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Eric - 1966 camper bus

"It's like, how much more black could this be, and the answer is none.......none more black."

[flatfour]