2001 GMC 2500HD trailer wiring

[KB9UDE]

I have a 2001 GMC 2500HD crew cab that I pull my 25ft gooseneck trailer with. It seems to not have any brake lights on the trailer. I have read online that it could be in my turn signal switch?? Has anyone ever found this to be true??

Trailer brakes and all other lights on trailer and truck work fine just no trailer brake lights. I have checked all connections. There is no voltage going back there on the truck.

 

[George2615]

Do the turn signals on the trailer lights work or just the parking lights?
If the turn signal lights work then the brake lights should since they use the same filament in the bulb.
Also, check the fuse box in the truck. Some trucks have separate fuses for trailer brakes / turn signals. A friend of mine had this problem with a Ford. Everything on the truck worked but no trailer turn signals. Turns out he has separate fuses in the truck for the trailer lighting and two were blown..
If everything checks out with the truck but no turn signals or brakes on the trailer then the bulb filaments or sockets may be bad.

 

[Dmace]

I assume you have a 7-pin connector since you mention trailer brakes. I would go through with a voltmeter and check each pin while using the ground pin for a ground. Do not forget that if you are checking the turn signal or tail light pin then you need to have the turn signals on or have the lights/brakes on while checking.

Another thing is make sure you have AT LEAST 12 volts. I chased a problem for a while where my lights were not working but all the pins showed voltage. It took me a few minutes (and beers) to realize that I was only getting 11.6 volts to my tail light pin and that is not enough to illuminate the bulbs.

Here is the typical wiring diagram:

 

[Diamondpilot]

I would do as others have said and start at the truck with a test light and make sure all works at the 7 way plug. They gave very good advise.

GM does use seperate fuses but not 100% sure on that old of a truck. I know my 05 did because it would blow them frequently. If the trucks plug checks out then it has to be between the trailers plug and the light itself.

Chris

 

[Soundguy]

my 01 gmc yukon 1500 did that and it ended up being bad ground.. when the brakes engaged there was insuficient ground for the lmaps.. check that.. start at the plug as the others said.

might want to clean up the connectors and grease them.. perhaps install an extra frame to frame quick connect ground wire.

soundguy

soundguy

 

[Peej]

I know it may sound bad but have you checked the fuses. my 2000 GMC has seperate fuses for the 7 pin. I did not know that until last week. Went so far as to "jump" the wires to get the right turn signal on the trailer to work.
Someone told me about the seperate fuses for the trailer connector.
Under the hood with the rest of the fuses and Duh it was blown. Replaced fuse and reattached jumped line. Business as usual then. Just felt real dumb!
"momma always said.......... "

 

[KB9UDE]

I have checked the fuses and even cut all the splices in the factory harness where someone spliced in a 7 pin RV plug for GN in the bed. Checked wires on the supply (front) side and nothing for brakes.

 

[Soundguy]

does the controller show it is connected? it senses that thru the brake magnets / brake power line.

soundguy

 

[Soundguy]

most I know won't power the brake line without 'seeing' the brake magnets..

soundguy

 

[KB9UDE]

Electric brakes work fine. Everything works on truck, all but brake LIGHTS on trailer