Dash Lights not working
Thread Starter
Cruising
Joined: May 2006
Posts: 10
Likes: 0
From: Portsmouth VA
Dash Lights not working
I have a 1991 Vette and the problem I have not been able to diagnose is that All of the Dash/accessory lights do not work. The Dash Cluster illuminates fine, the parking lamps, and courtesy lamps work fine but things such as the Shift console light, AC control lights, Driver information center, Headlamp switch lights do not work.
I have power coming out from the headlamp switch when I turn it on and the dimmer switch seems to be working. I have also verified that all of the bulbs are good. I even pulled the dash cluster out to check for a bad ground as discussed in some other discussions.
Any thoughts.
I have power coming out from the headlamp switch when I turn it on and the dimmer switch seems to be working. I have also verified that all of the bulbs are good. I even pulled the dash cluster out to check for a bad ground as discussed in some other discussions.
Any thoughts.
Thread Starter
Cruising
Joined: May 2006
Posts: 10
Likes: 0
From: Portsmouth VA
Problem Fixed
I finally figured out what my problem was. After testing about 100 wires and connections I narrowed it down to a little silver heat sink looking box. It seems to be called the Incandescent Power Driver. I used the DX chart and found that my terminal B had no power to it with the parking lights on. I also figured out that if I put a jumper wire from terminal C to B my lights work. I am heading to the dealer to see if I can get a new one but, if I can't I will most likely leave it jumpered and wait to see if it effects anything else. Here are some pictures of the culprit.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
That little jewel you have there is either a self contained voltage regulator, or a transistor that is acting as a regulator which usually is driven by other electronics. I tried running the number but it is one of those GM part numbers and will not cross to a standard component. You might be on the right track, but I could not even tell you how to check it if I don’t know what is. If it is open it will cause your problem. You might check it on the x1000 ohm scale just to see if you get anything. Wish I could tell you more. 
Last edited by pcolt94; May 18, 2006 at 06:49 AM.
Thread Starter
Cruising
Joined: May 2006
Posts: 10
Likes: 0
From: Portsmouth VA
It was located up under the dash next to the steering column just behind the turn signal flasher. I got a new one from the dealer and put it in. Shazam, the dash lights work! The dealer told me that the early model cars 84-92 were experincing dash fires due to the dash lights heating up. GM put this in as a secondary rheostat/breaker to prevent the fires. He called it a "Switch-A M-Dimmer" Part# 1995263. Here is a diagram of where it is located.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Great work, good good for you. If I had to make a guess I would say it was a voltage or current limiting device of some sort. This is so you dont get full voltage to the bulbs so they run cooler. Bet it took some digging to find that one. 
On second thought it is probably a control device. It's like so you can pass a small current thru the rheostat which controls the device, and the heavy current for the lamps goes thru the device. This is to keep the rheostat cool and prevents heat and burnup. The device is designed to handle the heat. This system is used by all manufactures to control all kinds of things like fans and such.
On second thought it is probably a control device. It's like so you can pass a small current thru the rheostat which controls the device, and the heavy current for the lamps goes thru the device. This is to keep the rheostat cool and prevents heat and burnup. The device is designed to handle the heat. This system is used by all manufactures to control all kinds of things like fans and such.
Last edited by pcolt94; May 18, 2006 at 06:48 AM.
Thread Starter
Cruising
Joined: May 2006
Posts: 10
Likes: 0
From: Portsmouth VA
It never seems to end. This Vette was originally special ordered for a Japanese Millionaire who lived in Japan. A few weeks ago when I got the car there were 2 sensors coming out of the exhaust, one on each side. The wires were broken off on one so I figured I would replace them. When I too one to the parts counter, I had everyone in the shop trying to identify them. No one had ever seen them. So I deceided to remove them. I unscrewed them fro the exhaust and plugged the holes, began tracing the wires back to their origin and walaa. They went into an alarm module, then it hit me. They were Thermocouplers, if someone started the car, the heat generated would stimulate the thermocoupler and activate the alarm. Pretty Clever. 
