Need help with electrical issue

[4X4HIGH]

I'm having an issue where my interior dome lights on my 89 K5 stay on. I've checked the door switches (I replaced them about 2 months ago because the old ones were frozen shut and the dome lights wouldn't come on with the doors open) I made sure the headlight switch was not set to have the dome lights on. I also removed the headlight switch entirely and the dome lights still stay on. I even removed the fuse marked T/L Courtesy and they STILL remain on. I'm at a loss now. The only thing I can think possible is that I just replaced the engine over the weekend and while installing the bellhousing bolts I accidently pinched the HOT wire going to the starter that comes out of the harness against the firewall (battery was not connected at the time) when I was ready to connect the battery is when I discovered a dead short from the pretty sparks that were made when contacting the positive wire to the battery. I repaired the issue and did not see anything melted anywhere since I was very quick about removing the cable when I seen the spark. I know the door pins supply a ground to turn the dome lights on but does the headlight switch supply a ground also when using it to turn on the dome lights or does it supply a HOT?

 

[onetonbb74]

Constant hot to all the dome lights and the switch is the ground. Orange is hot and white is ground. It sounds like the white wire is grounded somewhere.

 

[Truckman4life]

 

[Wes Harden]

If you have any add on accessories, check the screws may have priced a wire and grounded the circuit. Also look for melty wiring under the dash

 

[4X4HIGH]

View attachment 357069

What year is that schematic for? I see where its saying "06 model"

 

[Truckman4life]

What year is that schematic for? I see where its saying "06 model"

I put in '89 blazer on AllData. If I remember the wiring runs under the sill plates.

 

[4X4HIGH]

I put in '89 blazer on AllData. If I remember the wiring runs under the sill plates.

That is definitely not an 89 Blazer schematic considering it is showing rear door switches. I thought about it this morning and the most logical place to start is at the rear cap inspection cover where you would disconnect the wiring in order to remove the cap and then work my way back towards the front under the door sill plate and along the corner of the floor where the wire bundle runs.

 

[frankin5]

@4X4HIGH here is a 91 version.

 

[4X4HIGH]

the door has a tube that the wires go through to get from cab to door(dont know what its called ) but inside it they break check there

I know what you're talking about but the dome light wiring doesn't go inside the doors.

 

[Kain]

good point

 

[4X4HIGH]

Last night I tore the Blazer apart looking for a shorted ground wire and could not find one anywhere. For now I just pulled all the dome light and courtesy bulbs out.

 

[Wes Harden]

Unplug the orange wire from fuse block or pull fuse, check for voltage on orange wire. If voltage is present you have a short to power. If no voltage present check for continuity from orange wire to ground with all bulbs removed. If you have any reading but infinity you have a short to ground.

 

[4X4HIGH]

Unfortunately not how the done light system works. The orange wire goes between the fuse block and is not removeable and is a constant HOT wire at all times. GM used ground to complete the circuits. The issue I have is that the white wire (ground) is shorted out to chassis ground somewhere in the system and I cannot locate where just yet.

 

[Wes Harden]

Has to have a fuse. And my 77 is unplugable, at least part of it the Silverado add on for sure

 

[4X4HIGH]

There is NO fuse, I believe it may be a fuseable link wire instead.

 

[Wes Harden]

T/l ctsy fuse is fuse for dome lamps

 

[4X4HIGH]

T/l ctsy fuse is fuse for dome lamps

NO it is for the footwell courtesy light.

 

[Wes Harden]

Same circuit afik, light switch only provides a ground.

 

[Wes Harden]

See the red wire from #2 cavity on bulk head plug, it feeds the t/l ctsy fuse. If that fuse is pulled the circuit, orange wire, will be dead past the fuse block. The red wire at cavity 2 is feed by the fuse link at starter or juction block on firewall.

Circuit 140.8 is plugged in at top of fuse panel also feed from #2 bulk head red wire

 

[4X4HIGH]

The taillight courtesy fuse supplies voltage to the headlight switch and then when you turn the switch counter clockwise you complete the ground circuit for the courtesy light only

See the red wire from #2 cavity on bulk head plug, it feeds the t/l ctsy fuse. If that fuse is pulled the circuit, orange wire, will be dead past the fuse block. The red wire at cavity 2 is feed by the fuse link at starter or juction block on firewall.

Circuit 140.8 is plugged in at top of fuse panel also feed from #2 bulk head red wire

I have pulled the T/L courtesy fuse and the dome lights AND courtesy light still remain on. I have actually pulled ALL fuses and circuit breakers one at a time and NOTHING kills the lights because it is short to ground on the white wire somewhere in the system.