clearance lights come on when braking?

[TMitch]

Just got a call from my father-in-law who has a 04. 5' 3500 DRW 4x4. He said that today he was parked with the engine running, headlights off and stepped on the brake pedal and noticed in his mirror that the side rear fender clearance lights came on whenever he stepped on the brakes. Further investigation shows this happens engine on or off to all the clearance lights (fenders and cab). Where do we start?

 

[jelag]

You've either got a forward control module problem or a ground circuit problem... .

If someone has worked on the truck and removed a ground strap the brake light circuit is hunting a ground through the tail light filaments... assuming that both the brake lights and the clearance lights are coming on... .

IF only the clearance lights come on and no brake light's its the module... . geez hope I have the name of the correct module... but you get the picture...

If you changed batteries, or have done any other work, check those connections. . it could be as simple as a bad ground on one battery... .

 

[TMitch]

Thanks Jim,
Brake lights come on and the clearance lights too.
He says the ground straps have never been touched.
He did say he had a problem with one of the taillights this past summer and changed the bulb as well as smashing one of the tailgate clearance lights which may now have water in it. He's going to unplug the tailgate lights and to see if he can eliminate the taligate lights as a problem and report back.

 

[fkovalski]

Use the KISS principle- Check and perhaps install new tail lamp bulbs.



I actually had this happen as a customer complaint when I worked years ago at Chevy dealer. The complaints were just as you describe and more. The element in one of the tail lamps broke loose, fell and crossed over connecting to the other circuit all inside one of the bulbs. All sorts of weird things were happening when the brakes were applied.



Check this possibility... it may be an easier fix than you think.

 

[seafish]

The element in one of the tail lamps broke loose, fell and crossed over connecting to the other circuit all inside one of the bulbs. All sorts of weird things were happening when the brakes were applied.



.

If your FIL has a broken clearance lamp and there is water in it, the water is likely connecting different circuits to ground, just like fkovalski loose filament was doing... definitely casue all sorts of problems with where current flows to AND through and what lights up as a result. get the water out, dry and clean the socket (or replace it) on the broken clearance light, replace the lense with an unbroken one, and I'll bet his lighting problems just go away. It's probably much easier and hopefully cheaper just get a replacement clearance light assembly and install that, but if it costs to much, you could troubleshoot jsut by drying and cleaning the one the broken one and seeing if that fixes the prob. Good Luck. . be sure to let us know what the fix was...

 

[mwilson]

Trailer plug socket could be full of green stuff also, have seen those backfeed before. Also check connector behind the trailer plug.

Is truck exposed to winter road clearing chemicals in B. C. ???

 

[TMitch]

brief update

He unplugged the tailgate clearance lights and no change... so that's not the problem. It might be a day or 2 before we can look at it together, big rain/windstorm here right now, and the forecast is calling for one more day of 50 knot winds and rain...

We are going to change the taillight bulbs next and if that doesn't fix it we'll dig into the trailer plug.

Thanks for the help so far.

 

[fkovalski]

Any update?