Need to upgrande trailer brakes

You will need to check voltages throughout the system to determine where voltage is lost. If you have 12V on the brake light circuit at the plug but no brake light on the trailer, there is a problem with the trailer wiring. If you do not read 12V on the trailer plug on the brake light circuit but you have working brake lights on the vehicle, there is a problem with the brake plug wiring on the vehicle.
DOES YOUR VEHICLE HAVE A SEPARATE REAR BLINKER CIRCUIT AND BRAKE LIGHT CIRCUIT? If so, you will need to purchase an adapter in order to use a standard trailer plug.

There is a fuse box under the hood that has the fuses that control the wire harness. There are at least 2 boxes, mine were on the drivers side wheel well near the rear of the engine compartment.

Look at the harness on the back side of the fuse box under the hood. Pull the fuse cover and the fuse box housing. You will probably have to remove the fender brace. They usually run the wires to connect to in the harness and bend them back into the wrap. Should be orange and blue. You will have to splice into them under the hood and run wires into the cab along with a GOOD ground and the drake switch and a hot fused wire. Look at the owners manual and see if fuse post 1 and fuse post 2 are connected. If not, one will feed to the brake controller and the other to 12 volt power to the trailer... Blue brake and orange to trailer power.
Also look at http://www.etrailer.com/faq-wiring.aspx. Full of useful info.

There is a relay/fuse box under the hood the max fuse for this is in there.

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.

Sometime around 2000, GM started putting trailering pre-wire harnesses in the vehicle. Your truck may have this harness built in and would greatly simplify brake controller installation. Look under the glovebox and see if there is a wire harness tied off. There will be four wires in this harness, which should be run over to the steering column to use it. Most trailer brake controllers are compatible with this harness.
The four wires in the harness are: Red, 12vdc; black, ground; blue or purple, brake pedal; and brown or white, trailer brake wire to seven pin, four pin, or five pin connector at trailer hitch, if your truck came from the factory with a trailer hitch.
If you are adding the hitch and do not have the four wire harness, the under hood wires from your brake controller are Red, connect to one of the studs under the distribution box cover (the distribution box is on the driver's side against the firewall. Underneath the cover are two large threaded studs which are hot from the battery all the time); and the other wire from your brake controller would have to be run the length of the truck along the frame, tied off in several places, to the trailer hitch connector on the bumper. Follow the directions that came with trailer hitch wiring connector to connect this wire to the proper pin in the connector.
If this has helped you, great, and please remember to vote/comment.
Good luck!

seperate fuse box under hood some time, alldatta is in your library

most new trailer brake units dont splice into the lines anymore they have vehicle specific plug that connects in line with brake harness under dash or under hood

It sounds like your have may have your brake light and running lights crossed on your wiring harness to the trailer. Good luck and hope this help's

Ask dealer if it has a towing package on it. If it does, you usually just pop fuse in under hood for electric brakes, and harness to adapt into is usually near or at rear bumper. Even if it doesn't have brake wire, you should still be able to install adapter at rear,for lights etc. which is available from dealer or auto supply places, then you may have to run electric brakes separate.