inertia switch

The inertia switch is in the trunk. If you take out the drivers side back curved panel it is behind it.

Just find the fuel pump wiring that runs near the drivers seat, or run the wiring over to the seat, and put your switch in under your seat, its a lot more convenient to just reach under and flip it. Or do both I guess (under seat and in the trunk), I am going to put it in a starter and ignition switches too to triple proof it.

On 86- 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.

Note that the wire colors changed in 1991, so there are two different descriptions.

86-90 model cars:
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. Using the control side of the circuit allows you to use light gauge wire and light duty switches. There is less than 1 amp going through the circuit, so you don’t have to worry about voltage drop across the wiring depriving the fuel pump of electrical power.
See http://www.autozone.com/servlet/UiB..._us/0900823d/80/16/71/3c/0900823d8016713c.jsp for 79-88 model wiring diagrams.


91-93 model cars:
Cut the Lt Blue/Orange 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 Lt Blue/Orange wire going to the fuel pump relay. When you are done the switch should be in the middle of the spliced Lt Blue/Orange wire that goes to and comes from the fuel pump relay. Using the control side of the circuit allows you to use light gauge wire and light duty switches. There is less than 1 amp going through the circuit, so you don’t have to worry about voltage drop across the wiring depriving the fuel pump of electrical power.
See http://www.autozone.com/servlet/UiB..._us/0900823d/80/19/59/5a/0900823d8019595a.jsp for 89-93 model wiring diagrams.

since we're on the topic...

has anyone tried using the fog light control as the switch for the fuel pump relay?

If you look at the diagram, you'll find that the inertia switch carries 15-20 amps of current in the 91-93 models. That means you have to use 14 gauge wire and and heavy duty switch. Do a poor quality job, or cut corners on the switch and wiring, and the fuel pump gets less voltage and less fuel output.

Do it the way I suggested and you can use 18 gauge wire and a light duty switch. That is because you are only switching the relay coil power which is less than 1/2 amp. It makes it easier to hide the switch and wiring. You are putting the switch between the relay coil and the computer. If you make the splices at the fuel pump relay as I recommended, it will work perfectly and you will not have any problems with voltage drop to the fuel pump.

Near the fuel pump relay, preferably within 2-3 inches of the relay. You can use crimp splices or solder & heat shrink tubing to make the splices. I like solder & heat shrink because it makes the best connection & neatest looking splices.

jrichker said:

Near the fuel pump relay, preferably within 2-3 inches of the relay. You can use crimp splices or solder & heat shrink tubing to make the splices. I like solder & heat shrink because it makes the best connection & neatest looking splices.

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Does it matter how long the wires are that you connect to the switch? Could you run them from under the seat into the console, and hide the switch underneath the ashtray?

89lxsport50 said:

Does it matter how long the wires are that you connect to the switch? Could you run them from under the seat into the console, and hide the switch underneath the ashtray?

Click to expand...

When you do the wiring according to the tech note, wire length does not matter. That's the beauty of using the relay coil side of the circuit. Long wires, smaller wires and light duty switches are just fine and cause no problems if you do a good job of wiring and installing them.

slow5poh said:

damn it. i hand the wiring all ran thru the firewall and to the relay all i had to do was crimp the wires and melt the heat shrink. but i pulled it out in the 100 degree heat yesterday cause i thought i could run it to a wire that went back to the pump. the reason i didn't want it under the hood was becuase i had to run it thru the drivers side firewall then back across the firewall and down to the relay, and i figured if a thief popped the hood he would notice my work and see where i tapped into the relay. oh well. i had my stang brocken into before and they stole like 200 cd's and ****ed up my ign. cyl. i like in a better area now, but i'm still paranoid. thanks for the info. :damnit:

Click to expand...

I run all the underhood wiring I do through heat shrink tubing and/or the black wire loom that is used under the hood. It makes for a very neat job and looks so much like stock wiring that it is difficult to spot unless you know 5.0's inside & out. I have a heat gun, so it does a first class job on the heat shrink tubing.