Fifth Avenue 1991 security alarm module trouble...
 

Hi, I'm a new member here who is looking for some advice to help a friend who does not use the computer. I've done a lot of work with the 80's and 90's General Motors cars, including in-depth electronics work. So while I am new to Chrysler, I'm not new to older auto electronics work. I hope to be able to see the car in-person in a few days, but want to get some ideas ahead of time; hence I am here requesting some info. In my searching, some general info has come up, but I haven't seen anyone confirm that they have solved a problem similar to mine.

The car in question is a 1991 Fifth Avenue with the 3.3L engine. My friend got the car in a non-running condition. I can't remember what was wrong with it, but it had sat for a long period of time. He got it running and all was well for a few months. Now, it has stopped running. He had a local shop look at it, and they said the antitheft system was preventing the car from starting. Whatever they did resolved the issue temporarily, however the car has done the same thing again now and the shop has been unable to get it started.

In reading online, it seems that the antitheft system uses switch contact inputs to tell it when the key is turned to the LOCK or UNLOCK position in the door lock cylinders. This is the arming and disarming mechanism. I am wondering if that circuit could be intermittent and causing this problem. In reading online, it seems that it's possible to get this system "hard locked" so that a certain command must be issued via the vehicle's diagnostic link to reset it.

So my questions are; is it true that special software / factory tools are needed to reset this? Also, once we get it disarmed, would it be possible to disconnect the LOCK (arm) signal wire from the door lock cylinders so that the system won't arm again? The car is not liable to be stolen and the alarm is far more a liability than an asset at this point in the car's life.

Thanks again sincerely for any advice you can give. I will hopefully be able to look at the car in-person in a few days.
Sincerely,
David

This is my second attempt to post this. The first attempt gave an error message, which disappeared before I could read it.

That shop probably performed a "hard reset" from disconnecting the battery...The steps can be found here somewhere and even on You Tube. If your "friend" is letting the car sit for extended amounts of time between uses, there is a more probable chance that the battery is weakening, and should be "load tested" with proper tester.BUT this can really "mess with the factory alarm system! I don't have manuals for something that old handy to reference to offer much on your "modding" the alarm system to help you there. Good Luck!

Thanks. Yes, the car had been sitting for long periods of time. I do know that the battery is not old (a few months) but that doesn't mean it's good... will check it out. I guess at this point my best bet will be a wiring diagram for the system so that I can test the door key cylinder contacts.

I'm going to keep browsing the site looking for info, especially wiring diagrams.

Sincerely,
David