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Cadillac Repair/1986 cadillac tail lights problem

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Expert: - 3/6/2009


Question
I have an 86 cadillac deville. The tail lights don't work when I have the headlights on. They work for turn signals and brakes. I checked all bulbs and fuses, all good. If there is a short somewhere, how can I find it?

Answer
Hi Shawn,

Tail lights are not on the same circuit as the brake lights and turn signals.

Turn the head lights on and see if the side markers work. If not, you have a problem somewhere between the junction block at the firewall in the passenger compartment on the driver's side and the tail lights.

I know normally these cars did not have trailer hitches, but occassionally they did. Trailer wiring is known for problems.

You said you checked all the bulbs and fuses or did you? It does not matter if the brake and t/s work. Bulb filiment for tailight could still be bad. If you pull the bulb, you will see the broken filiment right away. Chances of having two bad bulbs are rare, but possible.

You may want to look at the owners manual as well to see if there is another fuse box. I know on many caddys, they had another in the trunk.

Rob  

Cadillac Repair

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Rob Painter

Expertise

Alarm system questions cannot be answered on this forum. These systems are not what I can answer. Without being physically at the vehicle and not knowing what kind of electrical service has been done on the vehicle, there is no possible way to give an accurate answer over the internet. My expertise is in Ignition/key based anti-theft systems. These issues include GM VATS (resistor chip in key blade) PASSLOCK (MRD)-ignition lock rotation based, no special ignition key and the PKIII Transponder (computer chip in key) systems. These systems are not alarm based and are integral with the starting of the engine. This is why I cannot diagnose alarm problems without physically looking at the vehicle: Alarm systems are a completely different annimal than ignition key/lock based anti-theft system. Many alarm questions come from vehicles 10 years old, and since older, many hands that had been involved over the years.I am an expert in all GM factory (ignition/key based)systems. Alarm system questions pose to many situations beyond my knowledge as to what has been done to the vehicle over the years. Some guy may have actually wired the stereo into the alarm system. Who knows? Over my past 30 years in vehicle wiring repair, I have seen unbelievable wiring disaters done by guys that consider themselves "mechanics." I have seen stereos and alarms intalled using surgical tape. I have seen modules burn up, un-fused circuits, wiring jambed between the doors and even lamp cord used for a starter kill. To answer alarm questions over the internet without examining the vehicle is like asking; What does it take to remove a dent?

Experience

Education/Credentials-ASE certified. 11 years with a GM dealer and 17 years with a repair facility dealing with only the repair of theft recovered vehicles.

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