Fuel pump shut off question

[shawnster]

I have done this before but forget the wire that I used..I want to put a fuel pump cutoff switch in my 88gt (poor mans alarm system) I got a heavy duty switch with a round circle key, I want to mount the switch in the ashtray, what wire do I need going to the fuel pump?..I think the wires are under the drivers seat but I really cant remember..anyone here have done anything like this? Thanks!

 

[jrichker]

On 87- 91 cars the fuel pump relay is under the seat, 92 and later cars ,the fuel pump relay is under the Mass air duct on the passenger fender well. Cut the red/black wire going to the fuel pump relay. Splice a 16 or 18 gauge wire into the wire and connect it to one side of the switch. Connect the other side of the switch to the other end of the red/black wire going to the fuel pump relay. When you are done the switch should be in the middle of the spliced red/black wire that goes to and comes from the fuel pump relay.

 

[TheUser]

or you could do like i'm gonna do and do it between the relay and pump. That way, I don't always have to hit the switch for the pump to work, but if I want it turned off, I can turn the switch off and it won't get power even w/ key in. Otherwise, when the switch is normally left on, it will be like a normal circuit and the pump will turn on and off w/ key. See what i'm saying? In theory, this sounds good. I've thought about this a lot and actually was thinking about it tonight. I just don't wanna have to hit a switch all the time (most places I go, i'm not worried about my car being stolen).

 

[jrichker]

The electrical circuit for the fuel pump has two paths, a control path and a power path.

The control path consists of the inertia switch, the computer, and the fuel pump relay coil. It turns the fuel pump relay on or off under computer control. The switched power (red wire) from the ECC relay goes to the inertia switch (red/black wire) then from the inertia switch to the relay coil and then from the relay coil to the computer (tan/green wire). The computer provides the ground path to complete the circuit. This ground causes the relay coil to energize and close the contacts for the power path. Keep in mind that you can have voltage to all the right places, but the computer must provide a ground. If there is no ground, the relay will not close the power contacts.

The power path picks up from a fuse link near the starter relay. Fuse links are like fuses, except they are pieces of wire and are made right into the wiring harness. The feed wire from the fuse link (orange/ light blue wire) goes to the fuel pump relay contacts. When the contacts close because the relay energizes, the power flows through the contacts to the fuel pump (light pink/black wire). The fuel pump has a black wire that supplies the ground to complete the circuit.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

Now that you have the theory of how it works, it’s time to go digging.

Putting a switch in the Orange/Lt Blue wire or the Pink/Black wire means that you have high current running through the wiring and switch. That means you need to use 12-14 gauge wire and a switch rated at 15 amps or more. It also means that any connection not properly done is likely to overheat and drop the voltage available for the fuel pump.

Put the switch in the low current side of the circuit that has the inertia switch in it. You have your choice of using the Red/ Black wire (relay power) or the Tan/Lt Green wire (relay ground). Either one will allow you to use smaller wire -18 gauge and a light duty switch rated a 5 amps or so. The smaller wire and switch is easier to run and hide than the lager gauge wire and switch. It is also not so sensitive to the quality of the connections, so if your crimper did a not so neat job, it won't hurt anything.

Putting the switch in the Red/Black wire allows you to easily use a test light to troubleshoot the circuit. A green LED could be added to the relay side of the switch circuit to show when the switch was turned on.

 

[88mustng]

i have a kill switch on mine goin to the coil so it will crank but it will never turn over unless my switch is on. still i can always just leave it on if i want and it will work just like normal.