good luck

Use your meter at the truck trailer plug and run through all the lights to rule out the truck. When all checks well and still no lights, sand the ball and the inside of trailer tongue, hook up trailer to boat and check with meter between the tongue and reciever to see if you have a good ground. When you have a good ground try the lights. If you still don't have lights check all wiring and ALL bulbs, if they are wired in series then all bulbs must work not just some.PM me if you need help. Low voltage elect. is easy stuff to figure out.

" When all checks well and still no lights, sand the ball and the inside of trailer tongue,"

Why not just put a wad of coarse steel wool on the ball, hook up the trailer and drive around for awhile?

You need to check and see if you have the right bulb in the socket. The 1157 and 2057 bulbs looks exactly alike but are different and if switched by mistake, it will not work.

it would also be helpful to know what vehicle you are towing with,some if not all of the new vehicles have seperate fuses for trailer lighting....

My Chevy has three (THAT'S RIGHT 3) different fuse boxes. Did you check them all? I beat myself down for 2 days awhile back and came to find out I had missed one of those fuses. Be sure you check'em all.

i might have misunderstood. does the brake light burn when the light are on. if that is the case change the wires on the plug because the brake lights are burning and u can not see the tail lights.

I would take it to u-haul trailers they have someone there will fix your problem for 5- to 10 bucks..

first, don't sand the ball and tongue, it should be greased, the ground needs to be bolted to the trailer bare metal to bare metal (white wire)and the truck should be grounded (did it come with the trlr tow package?) white wire from plug to metal bolted to frame. if the trlr wire is exposed check it out for any breaks or bare wire that may be touching metal. probably not a ground thing if the brakes are working, the turn signals/brakes are the green and yellow, brown is the running lights, check the turn signals (turn on the flasher) if both work then look at the brown wires for breaks or chaffes/bare wire. if all else fails, get a rewire kit from academy and replace with the l.e.d. lights, much less amperage draw, better visibility, and only about 50.00 $. should have wire/lights/and all needed for total replacement. not that hard to do and if an older trailer not a bad idea for peace of mind.

Had a similar problem on my trailer recently, drove me crazy, even used a continuity tester to make sure there were no breaks in the wiring.(continuity testers are cheap, about $5.)
Guess what....... the ground wire, were it was connected to the ground in the car wiring was loose. After reconnecting everything works ok.
Hope this helps

I had three blown out on my chevy and I have Nitro also..yes check the fuse box under the hood.