Adding a fuel cutoff switch IS a very good idea. IMHO I had one installed in my 1993 SC400 (RIP!) , and my car was broken into while parked in a parking lot. They must of known about the problem with Lexus alarms and leaving the moonroof open (92-93). (note: ALWAYS close up ALL windows when parking. The some older factory alarms become disabled if the moonroof is opened. So I was told by the Lexus dealer. They have since fixed that problem).

Anyway, when I went to my car, the door handle, and ignition were on the ground ($1400 for repairs). BUT my car was still there. They obviously couldn't figure why the car wouldn't start since I had the switch hidden in the ashtray.

Added protection is always good, and that is a very simple mod to do. IMHO

Lee

 

Here's the answer to your question:

If you cannot determine the correct wire, see if you can go near the top of the gas tank in the back and look for wires coming out of the top of the tank. One of which powers the fuel pump. But at least there's less wires to eliminate to get to the right one. Remember, the fuel gauge sender wire is also jutting out of the tank.

If a thief really wants your car, it will go to the next similar car and not waste its time on yours. Go on with your project. That's a great idea. Time is a carnapper's enemy.