The right blinker and brake light on my trailer have not been working. I called Trailer Hitch Inc. in Redwood City to see if they would check it out. I'd never been there before, but they are close. They had me bring it in the same morning I called. When I got there, they identified the problem, replaced a bad fuse in my truck, and sent me on way in 7 minutes - no charge.
If you're on the SF Peninsula and your trailer needs work, I recommend these guys. There number is 650-368-2125.