Theft Deterrent Fox-3 Fuel Cutoff

Written by Drewski Thursday, 18 February 1999 18:00

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Electronics

You've spent a lot of time and money on your Mustang. The last thing you want is some hood coming and stealing your pride and joy. Drewski, a Corral Techboard regular has come up with an inexpensive and effective theft-prevention system. The installation disables the fuel pump on SN-95 Mustangs.

The circuit created in this installation will disable the fuel pump by simulating the activation of the "Inertial Cut-Off Switch." In the event of a severe accident the ICOS is designed to shut the fuel pump of your Mustang off. This prevents the possibility of the engine running after impact, or fuel spilling from ruptured fuel lines. This installation will utilize this saftey feature.

1 Take a look at the fuel pump inertia switch, located on the driver's side rear in the trunk, and make a note of the wire colors at this connector. One wire is brown, the other wire is green with a yellow stripe. You will be splicing into this green/yellow wire as it snakes through the passenger compartment.
2 Remove the plastic trim along the bottom of the door opening on the driver's side of the car. Gently lift the carpet and you will see the wiring harness running underneath the carpet. Pull up the harness and tear off the plastic wrap to expose the wires.
3 Look for the fuel pump wire (green with yellow stripe). MAKE SURE YOU FIND THE RIGHT ONE! There is another wire that is olive green with a yellow stripe that looks similar, you do not want to alter that wire!
4 For safety, you can verify the right wire with a volt meter. To do this simply:

a) Stick a safety pin in the green/yellow wire that you found in step 3). The pin must be deep enough to pass through the insulation.
b) Connect a piece of wire to the pin, long enough to reach the trunk.
c) Go to the trunk, and remove the inertia switch connector.
d) Set your meter to read RESISTANCE (ohms) and connect one lead to the inertia switch connector's green/yellow wire.
e) Connect other volt meter lead to the wire that you connected to the safety pin.
f) If the meter reads 0 ohms everytime you connect the safety pin wire to the meter lead, then you have located the correct wire. If the meter reads anything other than 0 ohms, you have the WRONG lead!
5 Once you've found the correct green/yellow wire, you need only splice in a switch to this wire. Because of the amount of voltage running through the circuit, for safety reasons, you should use a relay to activate and deactivate it. A 30 Amp 12VDC SPST relay is more than sufficient. :
a) Cut the green/yellow wire.
b) Wire both ends of the green/yellow wire to the 12V in and 12V out leads on the relay (it doesn't matter which lead goes where, as long as it's the 12V in/out connectors).
c) Connect a 5ft piece of wire with2 leads, like speaker wire, to the coil side of the relay, noting which wire is connected to the relay's ground side.
d) Snake this wire to your chosen hidden spot for the switch (I chose a small hidden spot near my ashtray).
e) Connect the ground wire to a nearby bolt, making sure the bolt contacts the car body
f) Connect the other wire to one connector on your switch.
g) Connect the other switch connector with a piece of wire, and route that wire to a 12V ignition source (any wire that produces 12V when the key is in the ON position will work (use the meter to verify).

 

ALL DONE! when the switch is opened, the car will try to start, but won't run. flick the switch on, and you're off and running. email me if you have questions. these instructions should work on the '94-'95 mustangs (and maybe newer ones). now, this isn't the only way to do this. some people like to splice the wire at the inertia switch at the trunk, and the route the wires into the passenger compartment. while this would work too, the disadvantage is that a SMART thief will look there FIRST! if a thief finds the relay (or the splice), it's a simple matter of running a jumper wire to bypass all your hard work. using my way, the relay is hidden underneath the carpet by the driver's seat, making it very hard for the thief to find it. of course, he can run a jumper from the battery to the inertia switch in the trunk, but he'd have a wire whipping around while driving your car :-) hope this helps,

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