ignition disable - using "run" wire?

Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=9803
Printed Date: July 22, 2025 at 8:05 AM

Topic: ignition disable - using "run" wire?

Posted By: aberson
Subject: ignition disable - using "run" wire?
Date Posted: February 20, 2003 at 1:48 PM

I am considering doing an ignition disable, but I'm kind of curious as to why everybody says to put the relay on the "starter/crank" wire (only powered when cranking), as opposed to putting it on the "run" wire (powered when car in "on" and cranking).

Assuming somebody pops the ignition or has a key to my car, if I have the disable relay on the "starter" wire, the starter won't even run, and they'll assume there's some sort of kill switch and start feeling/looking around for a bypass. If I have it on the "run" wire, they will hear the starter motor run, but the engine won't turn over (and maybe the dash lights won't come on, etc) and they'll probably just think the car is broken, or kill the battery trying to start it.

Is there something wrong with my logic? or something I'm missing here? Any reason not to put the relay on the "run" wire?

thanks

-adam

Replies:

Posted By: Chris Luongo
Date Posted: February 21, 2003 at 7:22 PM

The main difference is in reliability and safety. If something fails in your starter kill setup, the worst that will ever happen is the car won't restart after it's been parked.

If an ignition kill fails, the car's engine might stall while on the road. Losing power at highway speeds is never much fun, and if the driver is an idiot, he may crash. Plus, then you're stranded at the side of the road.

If you decide to do an ignition kill on your car, be extra careful to do a good job. Consider placing two relays in parallel, so if one should fail, the car will still run.

Posted By: floaterr
Date Posted: February 22, 2003 at 9:31 AM

Also in some vehicle (i guess mostly fuel injection) the method you describe allows for the fuel to be delivered to the cylinders unitil the theif gives up. Risking flooding and mostly fire.

If you really want that kind of safety you should kill the fuel pump if it's electric. If not then I guess you have no choice.

The theif will know that you have killed the ign if they know you have an alarm. If you connect the relay in "failsafe" operation then if he can get to the brain, he can cut the orange lead and your out anyway. If you use "failsecure" (bad idea) make sure you cut the ign outside and hidden so the guy will waste to much time under the dash and hopefully give up.

Good luck!