Courtesy circuit

[V_Kint]

1994 K1500 RCSB

I've been tracking down and repairing my truck's minor electrical gremlins for a fee weeks. Over that time I've replaced the tail light housings, the headlight switch, the turn signal switch, the dash panel dimmer switch, and cleaned up as many grounds and connections as I can think of. This has cleared up most of the issues, but I have one that I can't figure out.

The courtesy circuit fuse pops as soon as it's inserted, and the radio, dome, and third brake light are not working. The last thing I tried was to unplug both the dome and brake light harnesses under the dash and close the door. Still the fuse pops as soon as I insert it.

One unknown is the rocker switch located right under dash panel dimmer switch. It isn't labelled so I'm not sure if it's part of the circuit (dome switch or cargo light?). How can I bypass it to make sure?

What's my next move?

 

[Eveready]

Sounds like something is shorted to ground. The way the lights usually work is that there is always power to the light and the switch completes the circuit by providing the ground. Somewhere ahead of a light, probably one of the courtesy lights, the hot is shorted to ground which is why the fuse is blowing. Let us know what you found when you chase it down. A Voltmeter is your friend here. If you clip the negative of the VOM to ground and then probe with the positive side of the meter you should find continuity on the side that is shorted. You may need to cut the circuit in various places to determine which side it is on.

Good luck!

 

[joep88cheyenne]

You can also use your vom to test set it to DC volts scale above 12 volts, put fuse in and don't worry if it blows. Attach leads across the fuse and see what doesn't come on or does come on. Open door also.

The vom will complete the circuit and since you have set the scale up it will allow a bit of time for quick visual. Don't be slow as it will work like tinfoil over a fuse and smoke test wires.

 

[joep88cheyenne]

You can use the vom when looking for a bad fuse also. When leads are across a fuse and key is on ....no voltage is good fuse .... voltage is blown fuse. Electricity takes path of least resistance. Fuse is less resistance so no voltage shown on meter.

 

[V_Kint]

Sounds like something is shorted to ground...

Good luck!

You can also use your vom to test set it to DC volts scale above 12 volts...

Found a clue. Someone before me was trying to figure this out. Looking under the dash, the door switch on the drivers side has been unplugged. Looking for other stuff...

 

[89RCLB]

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Hopefully these diagrams will help you...

 

[V_Kint]

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Hopefully these diagrams will help you...

I was searching for those earlier and I appreciate it.

Fortunately I tracked down the culprit just a few minutes ago. I followed out the run for the footwell courtesy lights, and all of the wires had been crushed under the steering column mounting bracket.

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@joep88cheyenne
@Eveready

Guys, thanks for the guidance - you dragged me over the goal line.

 

[joep88cheyenne]

Glad you found it.

 

[Eveready]

Glad you found it and thanks to 89RCLB for the really handy wiring diagrams. Those have been labled and placed in my "Truck" directory where I keep various handy and useful stuff that I find on this board. By the time I get the truck sorted out I will have an entire reference manual with pictures in that directory. Good job by the OP in chasing down the problem and in constructing this very useful thread.

 

[Ivan90]

Glad you found it! I had the exact same thing, the courtesy circuit fuses kept blowing. I disconnected the cigarette lighter and the problem went away.