Trailer brakes lights dont work on my 2001 gmc 2500hd

question edited for clarity typos and spelling, break/brake, 'peddle/pedal.
Question move to model category.

Incorrect wiring or bad earths on the trailer (common issue)

https://www.google.com/search?q=2001+gmc+2500+hd+trailer+wiring+diagram

look at other lamp fuses, sometimes an seemingly unrelated fuse will be the power source for your non powered fuses.

if there is a power problem then the corresponding lights of the vehicle will out as well. If they work check where the harness is plugged in and check the connection.

It sounds as though you have either a frayed wire between the brake control circuit and tail/running light circuit of the truck side of the plug, or someone wired the truck side of the plug incorrectly.

Think about it. The parking brake lights come on when the controller is activated. More than likely the tail lights are also.

The tail lights are also going to come on when the headlights are on. This would cause the trailer brakes to be activated IF there is a short in the TRUCK side of the plug itself.

That's where I would personally start investigating, The truck side of the trailer plug.

Hope this helps.

Hello Carol, The 7 way is for use with a brake controller and/or a trailer that has electric brakes. The 4 way flat is a basic trailer plug connector.
Connect as follows:
Green wire- Connects to the vehicles right turn wire harness & provides brake light and right turn signal on trailer.

Yellow wire- Connects to vehicles left turn wire & powers brake light & Left turn signal on trailer

White wire- Ground

Brown Wire- Tail/ marker/ license plate lights

The Blue, Red & Purple wires on the 7 way will not be used on the adapter, those are for brakes.

I hope this information is helpful.

Standard wiring colors are as follows:

4-Way

5-Way

6-Way

7-Way

Green

Yellow

Brown

White

Red

Blue

Purple

Right Turn & Brake

Left Turn & Brake

Tail Lights

Ground

Backup Lights

Electric Brakes

Auxiliary Power
Green- Right Turn and Brake
Yellow- Left Turn and Brake
Brown- Tail Lights
White- Ground
Red- Reverse (Back Up) Lights
Blue- Electric Brakes
Purple- Auxiliary Power

It sounds like your green and yello wires are shorted together somewhere along the length of the harness. I would check the wires on the trailer first. Easier yet, if you have another trailer to connec or access to another to use for testing, connect to it and see if the problem repeats; if it does the trouble is in the vehicle's wiring.

How have you tested this? If you are just looking for the stop or brake light, you need to test by pressing the break and probing the same pin as the turn signals as the vehicle does not have separate brake and turn signals. However, If the problem is that you have no signal for the electric brakes on your trailer. You must have a brake controller installed. If there is one installed probe the blue wire coming out the back end of it and press the brake to be sure there is brake output. It is possible for a controller to go bad, and not output anymore.
I wrote an imformative article on diagnosing wiring problems. Click here to read.

There are separate fuses for the trailer turn signals.Make sure they are good.They are in the under hood fuse block.If they are then check for corrosion in the trailer harness wiring.Hope this helps.Good luck.

Hey Boon,

The pinouts for a 7-way plug are as follows:
Seven wire Trailer plugs:

Horse, stock or utility trailers:
White = Ground - 1
Blue = Electric Brakes - 2
Brown = Tail and clearance lights - 3
Black = Battery, aux power - 4
Yellow = Left turn/Brake - 5
Green = Right turn Brake - 6
Orange or Purple (not both) = Auxilliary or Reverse - 7

Recreational Vehicle:
White = Ground - 1
Blue = Electric Brakes - 2
Green = Tail and clearance lights - 3
Black = Battery, aux power - 4
Red = Left turn/Brake - 5
Brown = Right turn Brake - 6
Yellow = Auxilliary or Reverse - 7

In both cases 4 is battery and 7 is reverse, aux or not used.

Double check your wiring using these lists as a reference.

Click here for my post on Trailer wiring

This should get us closer to the answer.

Best regards,
Mike

You may have faulty wiring for your trailer lights. Look under the back of the truck where the wiring harness leads to the trailer wiring harness. Usualy it is a 3 way plug in the harness. Try unpluging the harness from the trailer wiring and just plug the other 2 wires into eachother
Hope this works for you!