Electric Fuel pump cut off Relay

LEJ · Posted: Sat Jun 03, 2006 5:40 pm Post subject: Electric Fuel pump cut off Relay

Somewhere else on this board, I posted a way to cut off your fuel pump using a brake light switch tied into your oil pressure sender.

I've come up with another simple way to install a fuel pump cut off system and it should cost about $4.00

Start by going to the auto parts store and buying a Bosch 20/30 amp lighting relay. It's the kind that's square and is black plastic.

It will have 5 terminals on the base.

Terminals 86 and 87a are wired together and they will attach to a """SWITCHED""" 12 volt positive wire. (Remember, it has to be switched))

Terminal 85 will go to your alternator light output located on your alternator or tap into the wire from beneath the dashboard.

Terminal 30 will go directly to the 12 volt positive side of your fuel pump. The ground wire from your fuel pump will remain grounded.

You may want to install a momentary switch someplace hidden and attach a 12 volt positive wire to one side of the switch and wire the other side of the switch to the postitive wire on your fuel pump.

If the alternator stops turning, the fuel pump will shut off.

!!!!This has a dual advantage, should your fan belt break and you're paying attention to lights or gauges, the fuel pump will turn off and hopefully, you'll stall the engine before you cook the cylinders.

The other advantage is a safety issue if you crash your car.

I'm not an artist but here's a wiring diagram
http://hometown.aol.com/ljowdy/myhomepage/sale.html
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kubelmann · Samba Member Joined: April 13, 2003 Posts: 3268

Hey.. We are very into the rotary electric fuel pumps and this circuit is very well thought out. Thanks. I am in the process of changine fuel delivery. This circuit is now a part of my plan. Again thanks. K-mann

bugninva · Posted: Sun Jun 04, 2006 10:17 pm Post subject:

this is a simple yet effective "safety"...been around for quite awhile though....Jim even posted it to his site in 99

http://www.nls.net/mp/volks/schem/pump.gif

LEJ · Posted: Mon Jun 05, 2006 4:12 am Post subject:

When I worked out the relay wiring, I thought to myself that someone out there has done this before, I just couldn't find a source.

sometimes we just keep re-inventing the wheel
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Captain Spalding · Posted: Mon Jun 05, 2006 8:41 am Post subject:

germansupplyscott · Posted: Mon Jun 05, 2006 8:55 am Post subject:

there is a better circuit and relay that uses an early watercooled fuel pump relay.

http://www.dolphinsci.com/relay.html

the diagram on that page is MIA, but basically the relay senses the points opening (via the coil) and triggers, turing on the pump.

the problem with using the alternator blue light as the trigger is that if your alternator or generator cacks, your pump stops working too. not so good. the circuit above is 100% fail safe but will let you drive with no alternator, which if you think about, you want to be able to limp along even if your charging system is busted.

the relay is available at a junkyard or here;

http://germansupply.com/xcart/customer/product.php?productid=16928
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LEJ · Posted: Mon Jun 05, 2006 9:47 am Post subject:

Captain,

Take a look at the relay drawing again, 86 and 87a are tied together and then both are connected to a switched 12 volt power source, in this case, the positive horn wire.

30 goes directly to the positive wire on your fuel pump and 85 is the "turn off" trigger obtained when the alternator light goes to ground. (this happens when the alternator quits working.

German,,,

I've seen and heard about the relay you're discussing. It too is a another great way to solve the "fuel pump" cutoff.

I'm not saying that my way is the only way, it's just another solution.
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kubelmann · Samba Member Joined: April 13, 2003 Posts: 3268

This is another thread that will be a great resource for future information sought. I would like to include these various circuits on the RoMTOC CD

If any of you who posted your circuit are willing to have that info included please send me your circuit information in a pmail ([email protected]) and I will add it to the CD and of course give you credit for the creation. Thanks

Captain Spalding · Posted: Mon Jun 05, 2006 10:59 am Post subject:

Hella makes a relay with built in fuse. Might make for a tidier installation.

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

LEJ · Posted: Mon Jun 05, 2006 11:03 am Post subject:

That's trick, Can you tell which poles are fused???
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kubelmann · Samba Member Joined: April 13, 2003 Posts: 3268

Great item!

http://www.expeditionexchange.com/xcart/customer/product.php?productid=18441&cat=249&page=1

I found the Hella Fused Relay H41510131 at the above web site

It says - Use this relay to create your own wiring harnesses. The integral fuse receptacle obviates the need to have a separate fuse holder in your wiring harness. The result is a simpler wiring harness and a cleaner appearance.

Price: $ 15.00

Captain Spalding · Posted: Thu Jul 20, 2006 8:59 pm Post subject:

After much reflection and re-reading this thread, there is something that perplexes me regarding LEJ's relay circuit which uses the generator light as a turn-off trigger for the relay and pump. If the pump can't run when the GEN light is on, how do you start the car? The GEN light is on until the engine is running. . .

bugninva · Posted: Thu Jul 20, 2006 9:09 pm Post subject:

LEJ · Posted: Thu Jul 20, 2006 9:47 pm Post subject:

He's correct, fuel in the bowl is sufficient to start the car. Look at my schematic and you'll also see a momentary switch. That switch is a bypass and allows you to fill the carb bowl should it run dry due to evaporation or if you should service the carb and drain the bowl.
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Heiferman

lqqkatjon

this is what we like to use on some electric fuel pump retrofitted engines:

https://www.revolutionelectronics.com/Products/Fuel_Pump.html

you can make your own stuff up cheaper, but this product works pretty well. I know a couple people who have been running this for about a year since they first discovered this product.

madster

Heiferman · Last edited by Heiferman on Tue Aug 13, 2024 2:12 pm; edited 2 times in total

doublecanister

mondshine

Lqq and Double are correct.

The Revolution Electronics fuel pump controller is the right way to do this job.

It is superior to the "Rabbit" relay because the prime time is about double that of the "Rabbit" relay, and more importantly, the reliability is much better (for loads up to 7.5 amps, which is way more than enough for any electric pump fueling a carburetor).

Bite the bullet, and run a single "back to front" wire, (18-20 AWG would be plenty) to bring the tach signal (coil terminal 1) to the controller (or a dash tachometer, if you want one). The rest of the wiring is all "up front"; easy to access and close to the pump.

Here's an old post:
https://www.thesamba.com/vw/forum/viewtopic.php?t=757944

Good luck


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