just joined first post. i just bought a 87 gt converted to mass air and wanted to install a toggle switch to cut the power off at the feul pump relay. there are four wires pink with a black stripe, this one is spliced and i think is connected to the computer for the conversion, a yellow with a green stripe, red with a black stripe, and a orange with a blue stripe. which wire should splice into to accept the toggle switch?

 

go in the trunk and pull out the inertia switch and examine the wiring colors connected to it.

 

the wires going from the fuel pump relay to the inertia switch will be the ones i splice

 

You should have two bigger wires that supply power to the pump; Leave these alone, biggest reason is because of the load that will be put on the switch.

Relays themselves are switches controlled by another switch. The starter solenoid is a good example of this. It requires a bigger gauge wire to power the starter, rather than trying to wire in a heavy duty switch that can support the high amp load & thicker wires, they installed a relay so you could use a small load switch to close the circuit between the two big terminals on the starter solenoid.

The fuel pump relay (aswell as the others) operate the same way. You have two bigger wires & two smaller. The eec controls when the fuel pump kicks on by grounding one of the smaller ones from the relay to close the switch. If you have a voltmeter you can find that one easily. After the key is turned to the on position & the fuel pump has primed. You'll have two wires going into the relay that have 12v. (one big one, one small one). Then you'll have two that don't have 12v (again, one big one, one small one) The big one that doesn't will go to the inertia switch & from there to the fuel pump.

The small one that doesn't have 12v is the one you're looking for. In every mustang I've wired it is tan/green (or yellow/green in your case) It should go from the relay to the eec. Personally I would recommend just splicing your switch inline with it so when switched on the eec will still be able to prime the pump instead of the pump running at all times when the key is in the on position.

The wire that you see a splice in for the conversion is so the eec will know that the fuel pump has power, it's not for the relay itself. If power is going through that line, the computer assumes the fuel pump is working correctly.

 

Thank you, I have a volt meter and will check. I will also splice inline as you suggest. Thanks again for your help, I was just about to put the drivers seat back in and forget the whole idea