fuel cut off switch using cruise control

hey i thought of a good rite in the open but hidden fuel switch . i want \my cruise control button which does nothing now to be a push on push off fuel cut switch. its a 94 civic with integra dash, ive been searching alot but havn't had luck getting it to turn pump on or off i've done alot of testing it with diff wires but i think i need a relay or sumthing in line because i have a feeling my problem is the switch not holding enough amps to turn it on ne help would b greatly appreciated i believe i need it to be 10 amps to turn on fuel pump

sorry for such long post just think this would b a real nice stealth setup

First off, find the circuit that controls your fuel pump.
If it's EFI, it might be the EFI/ECU that controls it directly, or via a relay.

Otherwise the pump is probably controlled via the airflap (switch) or charge circuit and a relay.

In either case, you at least least need to find that relay - unless you want to intercept the pump's wiring and insert a relay.

oldspark wrote:

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First off, find the circuit that controls your fuel pump.
If it's EFI, it might be the EFI/ECU that controls it directly, or via a relay.

Otherwise the pump is probably controlled via the airflap (switch) or charge circuit and a relay.

In either case, you at least least need to find that relay - unless you want to intercept the pump's wiring and insert a relay.

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i found the fuel relay no problem there i just need to know how i can make my switch to get enough power to turn on pump. and i want to make the wiring pretty much non evasive as possible so a theif wouldnt b able to just look under dash and c wuts goin on

i think i need my switch to activate a relay to turn the power to fuel pump. not just try to wire it inline like i have been trying unsuccessfully

A relay usually only needs 200mA or so to turn it on and most switches can supply that.

So, how it the relay and switch configured?

Does the switch supply (or switch) 12V or ground?

Is it 12V or ground that turns on the relay?

You are going to need a latching relay of some sort.  There is a diagram on this site under the relay section.  It is under Special Applications.  However I would not reccomend using this for security reasons.  If there is ever a failure, and you happen to be pulling out in front of oncoming traffic, it may not be nice for you or your car.  Just some food for thought.

12v turns on my factory fuel relay i believe but i want to bypass relay due to hondas always killing them ne ways lol

Yes, idiots like me and idiot know that 12v is used to turn on a fuel pump or its relay. In fact - often both - and both simultaneously AND at the same time.

But for the sake of argument, I was also thinking along the lines of a latching relay. (It's a simple circuit that uses and ordinary relay.)   


But as Idiot Esq. says, there are reliability concerns.

And make sure you don't try powering a grounding circuit or vice-versa.
If it's your ECU (EFI computer) that controls the fuel pump, you might blow the ECU.
Whilst that is a very effective theft deterrent, unfortunately that will happen long before you have problems with thieves.

i never called u an idiot man .... dont' know were at u got that from if i was a all rightchous wiring guru i wouldn't be here askin u guys for help nd no the relay tells the pump nd the ecu to turn on i believe . i guess i'll jus do more reasearch and figure it out on my own thank u though   at least i have an extra harness if i melt thjis one

I didn't say you called me an idiot. I merely said that idiot like me knows that 12volts is used to turn on a relay.

If you meant that it is a +12V signal that turns on your relay, then I failed to understand that - I thought you were merely re-stating the obvious.
Nor could I understand wanting to bypass the relay "due to hondas always killing them" (any ways) if you were after a fuel-pump inhibit circuit. A bypass is a separate function to an inhibit (though they could be combined in one circuit).


But for the inhibit function, you can use the following circuit where the relay sits between the pump's +12V supply and the pump.
After initial power on, the relay is off until a momentary Normally Open switch - when pushed - supplies +12V to the relay's coil.
The relay then keeps itself on until both +12V sources are removed - ie, the EFI turns off the pump, or ignition off.


(yet again, dwg thanks to izu.)


And I wasn't worried about you melting harnesses or fuses, I was more concerned with ECUs or charge & air-flap devices being destroyed.

thank you nd i really didn't want u to think i was callin u a idiot lol. i think that is wut i'm lookin for i believe thank u very much one more ? is that push button used in the diagram one that pushes in and springs back out . Or is it a push in stay in type until u push it again ..because i have the 2nd one don't know if it would change how it switch

now if i understand i'll have to turn key on and until i push the button the fuel pump will not turn on . now if i push the button it will stay on until i turn off the car . so if i pushed the button off while driving the pump would stay running ? until i turned key off

Note - a diode (or 2) should be added to the circuit, but more (or changing the dwg) later...

It's a "momentary" on push button - ie, it is on "momentarily" only whilst you push it.   
So yes - as you described, spring loaded & stays out. It does not stay in or toggle (change over) a switch connection )ie, push-on, push-off, push -on etc)

The circuit requires the "12V source for pump" to be +12V. Without that, the relay will not latch on (ie, stay on).
I'm assuming that is with ignition on and the car ready to go etc.

With +12V available the "Push" switch, a momentary on with energise the relay - ie, energise the solenoid/coil and pull the upper contacts closed. (The push must be long enough to close the relay contacts - usually much less than 1 second.)

After the above, the +12V "Pump source" is conected through to the fuel pump AND also the relay coil, thereby keeping the relay energised and keeping the pump on.

The only way to open the relay to stop the pump is to either break that feedback connection (pump's +12V to the relay's coil), or remove the +12V "Pump source" - ie, either turn off the ignition, or the car's own fuel pump control has shut it off (hence you do not override the car's off control).

One problem - the momentary switch will supply power to the pump. This could burn out the switch etc.
Likewise, with te +12V Pump source & relay on, there is +12V supplied to the relay-side of the momentary switch. This is no problem unless the momentary switch's +12V is a different supply etc.
Those problems are fixed by inserting a diode in each side of the relay coil's top "T". I'll do that later....


Another problem - if your car is EFI, you can probably probably crank the engine with the fuel pump off.
That means the fuel injectors are dry whilst pulsing open & closed and this wears the injectors.
It can also introduce air into the injectors etc, but that should be blead out - it might just mean a bit of extra dry, or misbehavior for a while.

If it's a carby car, the engine will probably start and run until the fuel bowl runs dry.
This could place it in a freeway or road etc.
But otherwise it is a good occurrence because any would be thief can usually pick and engine or start kill system and can usually easily defeat it (most people have no idea how easy!), whereas a stall and no start after a short run could mean some problem so they leave it. (In the freeway, or on the railway crossing.)   
A local anti-theft circuit many years ago used that principle - a simple timer would kill the ignition every 20 seconds or so until it was defeated. First stall - ok, it stalled; 2nd stall... hmmm; 3rd stall "To heck with this, this car is fudged!"

Anyhow, they are some considerations for HOW to "kill" a car - or not.

Updated diagram.
I wish I could delete the old one....