1999 Dodge Ram 2500 Q&A
1999 Dodge Ram 2500 Question: Brake lights don't work on truck or trailer.
Check for 12 volts at the fuse. A good fuse means nothing if no voltage is present. Fuse #13 (20A) in the Power Distribution Center powers up the brake lamps switch. Equally important is checking the lamps ground circuits. All else checking out ok, replace the brake lamps switch. - Johnny Mopar
In the front drivers side under the cab you will find where the electrical harness comes out of the cab. There on the cab side should be a light blue wire which is the brake signal to the trailer. Make sure on the plug that attaches to it there is a light blue wire going to the back of the truck. This wire was omitted on my truck! Bought a brake system for mine even though it came with a towing package it didn't get the blue wire! I had to splice into the wire and run a wire to the back. Hope it helps - pistolgrip