1988 K2500 courtesy lights/dome light problems

[Firewood truck]

Hello everyone.

I'm trying to track down an odd issue with my beater truck. It appears that the over head map lights/dome light don't work and the lower dash curtsey lights & glove box light are constantly hot. I will start with, I have downloaded the great wiring diagrams that are posted in this site. After a bit of studying them on Sunday, I realized that the 30A circuit breaker fuse was missing, so I got one of those and still have no over head lights. I replaced the bulbs and checked with a test light ( quick and dirty) and then my multimeter, no voltage going up there. I noticed that both lower dash courtesy bulbs were blown. I checked them and found that they are constantly hot ( 12V going to them).

Today I started with isolating the lower light circuit by unplugging both door jamb switches, no change- still getting 12V to those bulb sockets. I tried with all positions of the ignition key, no change. The ignition switch ( on the lower steering column is new, as is the ignition switch/key. Both were so worn out when I got the truck, you didn't need a key to twist the ignition switch)

By using the schematic, I traced the wires back to the Convenience Center, both sets of orange wires are always hot. I would imagine that the circuit needed to be triggered/completed by one of the door jam switches. I haven't pulled up the door sill trim to check for crushed/shorted wires, but outside of doing that, it really baffles me how 1/2 of the circuit is dead and the other 1/2 is constantly energized. I also pulled the aftermarket deck, expecting to find a hack job of the harness but I was surprised to find some nice, neat Crutchfield style harness that plugged into the OE harness. I can't see any evidence of hackery anywhere under the dash, no chew marks from critters, no chaffing of harnesses against metal. No pinched harnesses that I can see. All cluster lights work along with the dimmer. When I "click" it to the interior light position, it get nothing.

If anyone has any ideas on some more in-depth trouble shooting, I'm willing to try anything.

 

[Spareparts]

I THINK the interior lights are always 12V powered. When a door is opened it makes a ground connection and the lights turn on.
I also can not figure out how to make mine work either. The floor lights will come on with the dash switch but nothing else and never when a door opens.

 

[Firewood truck]

I THINK the interior lights are always 12V powered. When a door is opened it makes a ground connection and the lights turn on.
I also can not figure out how to make mine work either. The floor lights will come on with the dash switch but nothing else and never when a door opens.

Thanks for that info, it helped on the trouble shooting. Have you tested the door jam switches? When they go bad, it can keep the lights from turning on.

The schematics that I got from this site were very helpful. I got power up to the overhead courtesy lights, I'm just not sure if they are supposed to come on when the doors are open. I got the lower courtesy lights working with doors and the dimmer switch, the upper light is odd ( at least to me) I can turn on one side ( map light) or the other, but if both get turned on the big middle bulb lights up. It goes off when I door is opened, so it only works with the door closed and either by the dimmer switch or the little black buttons on each side of the housing.

I'm not 100% what my issues were, once I installed new bulbs in the lower courtesy light sockets and jumped the harness that plugs into the door jam switches, they started to function. I then swapped out the dimmer switch and that let them turn on from that switch.. That's when I probed the overhead light again and saw current on the orange wire. I reinstalled the light housing and got the lights to come on, although I'm not sure if they're functioning properly. Small victories!

 

[GoToGuy]

You need to 1) read the owners manual on function of interior lights. Not " circuit breaker fuse ". Silver metal small box Lego size in fuse box is a " self resetting Circuit Breaker ". The glass tube, or different colored " fuses " are one time use. Not " triggered" , when door is opened door switch " grounds completing the circuit, or ground powered.
2) Have you downloaded the free OE service manuals with the complete wire diagrams. If not you should. Has the answers.
When using the " reading / map lights next to the overhead dome light, with both map lights on, the dome light should not. The dome is either door operated or headlight/ dimming rehostat switch operated.

 

[Firewood truck]

@ GTG- thanks for the reply. Unfortunately the owners manual didn't come with the 35 year old truck. I have downloaded the wiring diagrams from this website, as mentioned. They didn't come with a self diagnostic tool, so I ask for help when I need some clarification.

Thanks for explaining how the dome lamp should function, it's been at least 20 years since I've owned one of these trucks. I thought that the upper dome should come on when the door is opened, but I just couldn't remember. I need to probe the white wire at the light housing to be sure that it has current flowing, but I'm betting that it's the "chips" above the switch or the switch itself, it's as if current is bleeding through to the big bulb. LMC has new ones, it's not worth $120 to me to get a new one, so maybe it will be a junkyard part the next time I go shopping for GMC parts.

 

[GoToGuy]

I don't know what a self diagnostic tool is. If you downloaded the service manuals the diagrams, ground locations, switches are there. We give the info but you have use the test light . Testing for power and grounds can take a little digging. Just like if took it to a shop.
What " chips behind the switch" ? Just two pushbutton on off switches. The dome , somebody probably couldn't read that's why it doesn't function correctly. Taking shortcuts just makes it harder fix things later on.
If you want a PDF of the owners handbook for your year. They can be had at the GM heritage website, they have a lot of books, manuals, handbooks, sales cards, that GM gave them from the Archives.

 

[Firewood truck]

You must be registered for see images attach

It took a bit of head scratching, but I got onto the trail of the root cause and found this. someone has been here before!

You must be registered for see images attach

Once I got the wires cut back to clean material, a good solder and shrink tube repair later and everything is finally working like it should. I did take the dome light down again, pulled out the buss bar and gave them a good cleaning to remove all of the oxidation. I used a dab of dielectric grease on the contacts and I was able to get some electrical contact cleaner down into the switches. The parts that I thought was electronic chips were actually just the tops ( bottoms?) of the push button switches.

Maybe this will help out someone else. The main issues that I had: the 30 amp circuit breaker was missing, 1 of the door jam switches was bad, the other was a bit twitchy. The broken wire down inside of the sill plate and the contacts inside of the dome light were corroded/oxidized. There was also a worn dimmer switch.

 

[Erik the Awful]

Good find!

 

[GoToGuy]

1 trucks getting older, 2 previous crap repairs make regular repairs make challenging 3 an open mind for repairs that could be out of the ordinary ( I'll just run a bunch new wires ) rather than repair what is the real cause.

 

[deleonjesse]

Hello everyone.

I'm trying to track down an odd issue with my beater truck. It appears that the over head map lights/dome light don't work and the lower dash curtsey lights & glove box light are constantly hot. I will start with, I have downloaded the great wiring diagrams that are posted in this site. After a bit of studying them on Sunday, I realized that the 30A circuit breaker fuse was missing, so I got one of those and still have no over head lights. I replaced the bulbs and checked with a test light ( quick and dirty) and then my multimeter, no voltage going up there. I noticed that both lower dash courtesy bulbs were blown. I checked them and found that they are constantly hot ( 12V going to them).

Today I started with isolating the lower light circuit by unplugging both door jamb switches, no change- still getting 12V to those bulb sockets. I tried with all positions of the ignition key, no change. The ignition switch ( on the lower steering column is new, as is the ignition switch/key. Both were so worn out when I got the truck, you didn't need a key to twist the ignition switch)

By using the schematic, I traced the wires back to the Convenience Center, both sets of orange wires are always hot. I would imagine that the circuit needed to be triggered/completed by one of the door jam switches. I haven't pulled up the door sill trim to check for crushed/shorted wires, but outside of doing that, it really baffles me how 1/2 of the circuit is dead and the other 1/2 is constantly energized. I also pulled the aftermarket deck, expecting to find a hack job of the harness but I was surprised to find some nice, neat Crutchfield style harness that plugged into the OE harness. I can't see any evidence of hackery anywhere under the dash, no chew marks from critters, no chaffing of harnesses against metal. No pinched harnesses that I can see. All cluster lights work along with the dimmer. When I "click" it to the interior light position, it get nothing.

If anyone has any ideas on some more in-depth trouble shooting, I'm willing to try anything.

Do u have pictures of those wiring schematic? Can u post them.