I will let someone else answer which wire to cut, but do have a couple of comments about switches. Back when I lived in the city (specifically, Detroit) years ago, I equipped every car I owned with a starter interrupt circuit. Mine were always of the relay variety, meaning that the switch itself only interacted with a relay, which in turn opened/closed the starter circuit, since GM starter circuits have always been high current designs. Some of the more fun designs I implemented were:

-- Cargo lamp on pickup truck, where you had to turn the cargo lamp on to activate the starter circuit. Beauty of this is that switch is a true rocker, and can be turned on before actually turning the key in the ignition.

-- Rear defog switch, where you had to turn on the rear window defogger to activate the starter circuit. Need to test the defogger circuit, since not all of them stay on during cranking, so the simple act of trying to start the car will disable the starter circuit Also, this requires the ignition to be turned to 'run', the defog button pushed, and then the car can be started. Stealthy, but 2-step.

-- Power window switch (raise mode) is kinda neat since you can do it without even your passengers knowing you have a bypass. Same principal could apply to a power seat switch.

-- Timer relay, not really a direct interrupt, but rather would let the car be started and moved, but shut off after 10-15 seconds. My thinking is that a thief, faced with a car that just quit in traffic is far more likely to bolt than to fiddle and try to get it restarted. Conversely, if he breaks into the car and it at first refuses to start, his first efforts are going to be to figure out why, and he has a few moments to do that when just sitting in a parking lot. Things change dramatically when he has already rolled the car out into the street.

Good luck, these are always fun projects.

 

Do you have the wiring diagram(explanation) on how to do the defogger switch and the power window switch type.What materials are need to do the timer shutoff. Thanks

 

Yikes, my ASCII art sux, so I will just have to attempt an explanation.

The problem is that I have not done this to the B-car, so I don't know what the rear defog behavior is like. You should test it with a light before you start cutting wires. Basically, there is a relay somewhere that is activated by pushing the button in the climate control panel. You need to find that relay and find the wire that feeds the glass heating element on the switched side of that relay. FSM will be invaluable here. Once you find that, probe it while you activate the rear defog. Then start the car and make sure the rear defog doesn't switch off. If it stays on, you are in luck and you can merely run a feed to power the starter interrupt relay from that wire. Very simple. Defog on, starter circuit activated. Defog off, starter circuit deactivated.

If the defogger switches off during start, then you have to either look into another power source or get a relay with a timer. There are many available, and I suggest just start with google. I like Omron and Bosch relays, but there are many other good ones as well. The ones with timers will just have a knob that you turn to set the time, generally in seconds. You will have to get one that you can set to stay on long enough to get the car started once the power disappears from the defog circuit. I am thinking on the order of 5-10 seconds (not that EFI cars take that long to start, but anything very close to the actual starting time will be annoying).

The beauty of the defog circuit is that it will shut itself off after some amount of time, so it doesn't matter if you forget it or not. The bummer would be if you start the car, leave the defogger on until it times out, then shut the car off and try to restart it. The defogger circuit might not stay on long enough to start the car if it has just timed out within the last minute or so.

If you get a relay for the starter circuit and have an image of the pinouts, I can help you with which wires to hook up with which terminals (make sure you get a relay that will handle the current of the starter circuit...20 amps maybe?). Be sure to email me directly in that case, since I don't read this forum all that religiously. Hope this helps.

 

Originally posted by Scott Knight:

-- Timer relay, not really a direct interrupt, but rather would let the car be started and moved, but shut off after 10-15 seconds. My thinking is that a thief, faced with a car that just quit in traffic is far more likely to bolt than to fiddle and try to get it restarted. Conversely, if he breaks into the car and it at first refuses to start, his first efforts are going to be to figure out why, and he has a few moments to do that when just sitting in a parking lot. Things change dramatically when he has already rolled the car out into the street.

Guys,
One neat trick that I did in my old truck along these lines is wire a switch to my electric fuel pump. It would start and run for a few seconds on the fuel that was in the lines, but quickly stall out. The truck was broken into twice in 2 months, but was still there when I got back!

Cheers,
Jeff

 

There's a button on the dash that really never gets used: E/M. That's just begging to be used.