TheSamba.com :: View topic - Simple Cheap Electric Fuel Pump Safety Switch

Sat May 18, 2013 6:22 am

I would like to address a super simple fuel pump safety switch I installed on a friends bug...after a lot of research and finding a lot of confusing wiring diagrams using the SP-64 oil pressure safety switch I had found a much simpler way of doing this...bear in mind that I have no pictures yet and will work on doing a wiring diagram for those who do not under stand my explanation.

I will be pulling power from the starter with a in-line fuse, a #10 wire thru a 30amp relay to the electric fuel pump...just follow the load side of the relay wiring diagram.

I went down to the local bug shop and purchased a brass tee fitting a new oil switch and a new 2 prong brake switch...the brake switch is the same thread as the oil switch...the brake switch will act as my safety switch to control my ground on the low voltage side of the 30amp relay.

The next step was to run a 16ga wire from the keyed on coil positive thru the low voltage plugs on the 30amp relay...on the output side of the relay run a wire to the brake switch and from the other spade of the brake switch run a wire to ground.

The purpose of this wiring design is 1. it does not put any extra load on the ignition system as the fuel pump is pulling power directly from the battery thru a fuse...and 2. the low voltage side of the relay only pulls less then 1/10 of a amp to activate the relay which will not put any extra drain on ignition coil positive.

The way the system is designed is simple, put key in ignition and turn the key on, no fuel pump running...there is plenty of fuel in carb bowl to start the car without the pump running...once the engine is started the oil pressure will cause the contacts in the brake switch to close which will start the fuel pump running, hence...if the engine is in a accident and the engine looses oil pressure the fuel pump will not run...if you get in your car and turn on the key and sit there talking to a friend for 10 minutes the fuel pump will not be running until you crank the engine and build up the oil pressure.

One other thing I did install was a toggle switch to ground...coming off the same side of the 30amp relay that you wired to the brake switch, run another wire to a small toggle switch , single pole 15amp type and run from the switch to a ground source...this will allow carb changing and will allow you to prime the new carb once installed without getting in the car and cycling the key on and off, just hit the toggle and cycle the accelerator pump on the carb until you hear the carb squirt fuel and shut the toggle switch off...now your ready to go.

Will be posting a wiring diagram soon.

VeeWee :D

Sat May 18, 2013 7:24 am

http://www.speedyjim.net/schem/pump.gif

This is an effective way to safety wire an electric fuel pump,with way less hassle ( no oil pressure senders,ect)..and it has a pushbutton override to allow you to prime if you need it.Use a quality rotary fuel pump and never have a fuel delivery issue again..I take extended trips in mine with temps of 90 plus in the summer,I used to carry a spare mechanical fuel pump due to occasional 'vapor lock' (actually the check valve sticking in the cheap pumps due to heat) went rotary and my fuel issues are over..

go to the junkyard and get a mechanical fuel pump block off plate from a vanagon...yep,vanagons are worth something..

Sun May 19, 2013 5:35 am

That wiring diagram shows the pump running when the key is turned on...I don't see how your way is better or safer...my design not only uses stock VW parts but will only operate when there is oil pressure present.

VeeWee

Sun May 19, 2013 6:40 am

veeweeman wrote: That wiring diagram shows the pump running when the key is turned on...

The wire connected to D+ on the alternator will be grounded unless the
motor is actually running and alternator putting out, so the pump will be
deenergized when the engine stops (or the alternator craps out, or the
fan belt breaks, etc.).

Sun May 19, 2013 7:50 am

Actually the D+ wire is energized when the alternator is operating.I didn't post this as a superior system,just another way to do it..one thing that makes it convenient is all the switch wiring can be done behind the dash (I mounted the relay to the wiring cover bracket) other than the power wire for the pump itself..I mounted the pump on the frame head to stay close to the tank...electric pump push way better than they draw...I spent a few more bucks on a rotary pump instead of a pulse pump like a facet for stability in fuel pressure, in this case a constant 3.5 lbs delivery pressure...regardless of engine rpm or engine compartment heat..never have a fuel delivery issue again..

Mon May 20, 2013 4:35 am

Thanks for the tip on the electric pump...I have always used the facet brand myself and I guess never owned my car long enough to have 'em go out on me...you have any particular brand of rotary pump you like best?

VeeWee 8)

Mon May 20, 2013 5:51 am

If you already have a facet run it,it will work fine.I have a Carter rotary pump,but there are others..

Mon May 20, 2013 4:17 pm

You both have good designs and what I like about both of them is that you added an external switch to fill the carb bowl when it is empty. Many folks forget this and it is a pain to start the car if it has sat for awhile or you do a carb swap.