'91 Coupe: odd courtesy light issue

[alec2538]

Thanks again to those that chimed in on my "stuck rear stop lamp" thread! I'm happy to report that the issue was diagnosed and confirmed within 3 posts!

 

Now that that issue is solved, I have another to share with the collective: the interior lights are inoperable in my '91. Sort of...

 

Currently, only the under hood lamp and the vanity mirror lights are functional. I have no footwell lights, no dome light, no trunk light, no map lights (mirror mounted). Same response when pressing the interior light button on the keyless remote, however all the other functions are operational. Pushing the dash illumination switch to the "INT" position results in the same: darkness.

 

From what I can see, all the courtesy lights (save the map lights) are powered by fuse #2, correct? Not only are the courtesy lights fed by fuse #2, but a host of other (and functioning) systems get their power from said fuse.... leaving me stumped.

 

Anyone have any ideas?

[2seater]

I didn’t lose all interior lights but I lost the drivers door along with seemingly unrelated functions like the trunk latch and it turned out to be due to the under seat wire splices. 

[Ronnie]

Again, your '91 might be different from my '88.

 

Your problem could be a power issue (orange wire) or a control (ground) issue. To figure out the problem you describe on my car I would remove the dome light cover and check for 12 volts being present at the bulb. The bulb should have power all the time. To check that connect one lead of your volt meter to a good ground and use the other lead to see if you have 12 volts in either side of the bulb. If you have 12 volts at the bulb you have eliminated the fuses as the problem.

 

If you have 12 volts on one side of the bulb, you can ground the opposite side of the bulb and the light should illuminate. That will tell you that that either the BCM isn't commanding the light to turn on, there is a bad interior light relay, or a bad connection as 2seater suggested. There is always the possibility the bulb is burned out... 🙂 

[alec2538]

5 minutes ago, 2seater said:

I didn’t lose all interior lights but I lost the drivers door along with seemingly unrelated functions like the trunk latch and it turned out to be due to the under seat wire splices. 

 

I considered bad splices, but according to the wiring diagrams the last splice in the chain is the one responsible for the majority of functions powered from fuse #2. The interior lights are first in the chain.

 

1 minute ago, Ronnie said:

Again, your '91 might be different from my '88.

 

Your problem could be a power issue (orange wire) or a control (ground) issue. To figure out the problem you describe on my car I would remove the dome light cover and check for 12 volts being present at the bulb. The bulb should have power all the time. To check that connect one lead of your volt meter to a good ground and use the other lead to see if you have 12 volts in either side of the bulb. If you have 12 volts at the bulb you have eliminated the fuses as the problem.

 

If you have 12 volts on one side of the bulb, you can ground the opposite side of the bulb and the light should illuminate. That will tell you that that either the BCM isn't commanding the light to turn on, there is a bad interior light relay, or a bad connection as 2seater suggested. There is always the possibility the bulb is burned out... 🙂 

 

I'll make sure to check for +12v at the dome light, and then ground. I wish it was as simple as a burnt out bulb, but having so many out at once makes that a long shot!