Quote Originally Posted by MsgMills View Post
Before you replace the light it self....Check your fuse panel...If your vehicle has the Tow package then the Fuse panel will have an individual fuse assigned to each tail light on the trailer. I thought I was having the same problem until I checked my owners manual for my (04) F150...... The fuse panel has assorted fuses specifically assigned for the Trailer Lights.... Fuse's for the right side of the trailer and left side...and I believe for the Brake lights and running lights......... Check the Fuse Panel first to make sure it's not just a blown fuse....or A bad connection for the plug from the trailer to the tow vehicle.... Corrosion inside the plug will prevent a good connection and keep the light from working.....
Great advise. You can get a cheap volt tester to check, or move the other light over and test.
I would also replace both of them at the same time if one is out. Putting two different ones on there can shift the tail light/brake load and cause one side or the other to burn out faster. Keep the good one you replace as an emergency spare.