Cadillac Repair: Parking lights wont turn off, theft deterrent system, cadillac service

Question
Thanks Bill. I thought perhaps my owners manual had a typo because it lists the headlight switch and twilight sentinal switch on fuse 14 as well, yet the headlights function fine with both of these when the fuse is out. You said that your wiring diagram reflects this also though, so that makes me wonder whether the problem lies somewhere else and it manifesting itself with the lights, or if there is some bad info published by Caddilac in this area. Is the wiring diagram something I can purchase or is that something only certified Cadillac service folks can get access to? Thanks again.

Also, any thought on the fact that with the fuse out the door chime sounds as if the lights are left on. It is kind of making me think about the relay idea you mentioned....but I do not have the theft deterrent system as far as I know. I do not see the security light in the info center come on when I start the car and the lights turn on for the self test....and it is definitely never on when the car is off as it would be if it were activated.

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Followup To
Question -
Hi Bill,I have a 1992 DeVille that I ran into an electrical problem with last weekend. Suddenly the parking and tailights will not shut off. I do have the twilight sentinal and most times have not used the headlight switch since I bought the car last year. I pulled fuse 14 to get them to shut off so I would not run the battery down and assumed maybe I had a short in the headlight switch. I left the car with my regular auto mechanic and he looked into on and off over 2 days because he was quite busy and is not really an Auto Electric shop so is not an expert. He did disconnect the headlight switch to isolate that as the problem, but the parking lights still stay on. He also did the same with the twilight sentinal switch and the parking and tail lights still stayed on. The only other one he tried I am not sure of. I am not sure wheter he disconnected the Maxi fuse (because I see there is one that feeds fuses 13 and 14) or if he said a relay (I thought he said relay actually but did not see a headlight relay listed in my owners manual( I do not have a service manual). I have an electronics background and own a digital multimeter so I think if you give me some ideas I can probably troublsehoot this before deciding to go to a dealer or auto electric shop who will be more expensive. Just an FYI, my mechanic did not charge me anything for his time because he did not fix the problem ( a breed that I will miss when he retires later this year). Thank you for any input.
Answer -
Hi Tom, If you pulled fuse 14 and all the lights turned off then unplugging the headlamp switch and or the twilight sentinal module should have turned off the lights too because they  come off the fuse. The only other thing that could keep the lights on according to the wiring diagram is if you have theft deterrant and the relay is sticking closed then the lights will still get power. Sounds like you need to retrace his steps useing a wireing diagram to see where the problem lies. You are right it is rare that you didn't get charged something for his time. Bill

Answer
Hi Tom, Getting a wireing diagram shouldn't be a big deal. The dealer might make a copy of it if you ask. Otherwise a Chilton or Haynes manual can be bought at the auto parts store and they might have it. K-mart and some parts stores have a cd that you can buy and it has wiring as well as other service info on it that you can use with your home computor. Otherwise All Data has a 1 year subscription that will allow access to repair info and bulletins. Sounds like you are going to have to do some wire tracing because this doesn't sound like an easy fix. The only other suggestion is to check all the fuses in the fusebox because if one fuse is bad the power could be comming from another fuse and backfeeding the circuit. Physically remove each fuse and inspect it to make sure it is good or use a meter on it if not sure. Good luck. Bill