It has nothing to do with the bulb. [http://www.hitches4less.com/expedition-trailer-wiring-kit.html Go here for the Part You Need.] Good Luck and Remember.
Change Your Mind, Not Your Oil.
Use the First In Synthetic Motor Oil's.
See My Bio For more information.
Check parking/tailight fuse
It is for the trailer running lights.
Lights are required on a boat trailer to proven those from behind running into your boat trailer. This is especially important at dark where it is difficult to see an unlit trailer.
I would check the running lights for one with a short. I had the same sort of thing with my trailer and I spent way to much time troubleshooting the brake and signal wires. Turns out a running light bulb connector was grounding out on the trailer and messing it all up.
Lights are required on a boat trailer to proven those from behind running into your boat trailer. This is especially important at dark where it is difficult to see an unlit trailer.
Tail lights and brake lights fuse.
42
I have no running lights on my 2006 Peterbilt 387 all of the lights work
Short in the wiring. If you have a trailer wiring harness check it for frayed wires. The tailight circuit and the dash lights share a circuit on many vehicles. I hope this helps you. Mark
Fuse #9
Your trailer tailights are dual-filament, with one being the running lights and the other the brake lights. You need a separate power source from your towing vehicle's brake lights to power them. The easiest way to do this is go to U-Haul and but a set of their trailer towing taillight bulbs for your towing vehicle. The bulbs replace your standard tail/brake light bulbs, and they have two wires coming out of the base of the bulb. One of the wires connects to your trailer's running lights, and the other one connects to your trailer's brake light circuit. I'm trusting that when you re-wired your trailer, you ran two wires from the taillight socket, one for the running lights and one for the brake lights. In some trailers, the brake light circuit also doubles as your turn signals. Good Luck.
Try parking/tailight fuse