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mailman Samba Member
Joined: March 24, 2005 Posts: 1663
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Posted: Tue Mar 04, 2008 4:22 pm Post subject: Proper electric fuel pump wiring |
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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....
_________________ '64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop) |
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mailman Samba Member
Joined: March 24, 2005 Posts: 1663
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Posted: Tue Mar 04, 2008 5:58 pm Post subject: |
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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? _________________ '64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop) |
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akokarski Samba Member
Joined: May 24, 2004 Posts: 1896
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Posted: Tue Mar 04, 2008 7:25 pm Post subject: |
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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 |
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Glenn Mr. 010
Joined: December 25, 2001 Posts: 76909 Location: Sneaking up behind you
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Posted: Tue Mar 04, 2008 7:27 pm Post subject: |
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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.
_________________ 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
Last edited by Glenn on Wed Oct 16, 2019 5:22 am; edited 1 time in total |
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mailman Samba Member
Joined: March 24, 2005 Posts: 1663
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Posted: Wed Mar 05, 2008 3:50 pm Post subject: |
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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.... _________________ '64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop) |
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fluxcap Samba Member
Joined: February 07, 2006 Posts: 1969 Location: Newnan GA
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Posted: Wed Mar 05, 2008 4:09 pm Post subject: |
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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....
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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. _________________ Eric - 1966 camper bus
"It's like, how much more black could this be, and the answer is none.......none more black." |
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mailman Samba Member
Joined: March 24, 2005 Posts: 1663
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Posted: Wed Mar 05, 2008 7:15 pm Post subject: |
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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? _________________ '64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop) |
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mailman Samba Member
Joined: March 24, 2005 Posts: 1663
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Posted: Wed Mar 05, 2008 7:26 pm Post subject: |
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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.... _________________ '64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop) |
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mailman Samba Member
Joined: March 24, 2005 Posts: 1663
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Posted: Wed Mar 05, 2008 7:30 pm Post subject: |
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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? _________________ '64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop) |
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Glenn Mr. 010
Joined: December 25, 2001 Posts: 76909 Location: Sneaking up behind you
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Posted: Wed Mar 05, 2008 7:34 pm Post subject: |
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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 |
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akokarski Samba Member
Joined: May 24, 2004 Posts: 1896
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Posted: Wed Mar 05, 2008 7:34 pm Post subject: |
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mailman wrote: |
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? |
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 |
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mailman Samba Member
Joined: March 24, 2005 Posts: 1663
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Posted: Wed Mar 05, 2008 7:41 pm Post subject: |
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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..... _________________ '64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop) |
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Glenn Mr. 010
Joined: December 25, 2001 Posts: 76909 Location: Sneaking up behind you
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Posted: Wed Mar 05, 2008 7:44 pm Post subject: |
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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. _________________ 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 |
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mailman Samba Member
Joined: March 24, 2005 Posts: 1663
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Posted: Thu Mar 06, 2008 5:20 am Post subject: |
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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. _________________ '64 Bahama Blue Beetle / steel sunroof
'64 Bahama Blue Beetle Sedan (future ragtop) |
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1961bluebug Samba Member
Joined: November 11, 2002 Posts: 1137 Location: Czech Republic, Europe
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Posted: Thu Mar 05, 2009 4:00 am Post subject: |
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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.
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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? _________________
|82x94|
1961 Deluxe beetle, 1971 type 181, 1968 T2a Baywindow, 1973 Type 147 "Swiss Fridolin"(sold), 1966 Deluxe sedan (sold), 1983 "Silver Bug" edition (sold), 1961 beetle (sold) |
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[email protected] Samba Member
Joined: March 18, 2002 Posts: 593 Location: Peterborough, Ontario, Canada
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Posted: Wed Mar 24, 2010 2:05 am Post subject: |
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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.
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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... |
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fluxcap Samba Member
Joined: February 07, 2006 Posts: 1969 Location: Newnan GA
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Posted: Fri Apr 01, 2011 1:56 pm Post subject: |
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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.
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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 , 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!!! _________________ Eric - 1966 camper bus
"It's like, how much more black could this be, and the answer is none.......none more black." |
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canvmnvw Samba Member
Joined: September 04, 2006 Posts: 236
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Posted: Sun May 22, 2011 4:10 pm Post subject: |
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I beleve German Supply sells a socket for it |
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fluxcap Samba Member
Joined: February 07, 2006 Posts: 1969 Location: Newnan GA
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Posted: Sun May 22, 2011 5:31 pm Post subject: |
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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. _________________ Eric - 1966 camper bus
"It's like, how much more black could this be, and the answer is none.......none more black." |
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flatfour Samba Member
Joined: August 23, 2003 Posts: 688
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Posted: Sun May 22, 2011 6:09 pm Post subject: |
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I got one of those also and so far it's been working great. _________________ '68 Bug
'74 Ghia |
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