No trailer lights

If you have a test light make sure you have juice out the trailer cord, cord could be bad.
Process of elimination, where does the juice stop?

 

You may only have juice to those circuits. If only the marker light circuit is bad, the others will work.

 

Is this your regular trailer, or one you just picked up?

 

These are the reason for issues most of the time.

 

If you wiggle the plug do the lights come on? The biggest issue I had was a worn plug not making contact. You can stick a piece of plastic or folded paper in the side when you push the plug in to keep tension on it temporarily, and get a new plug or cord later.

 

If it's an older trailer with split pins, you can spread the pins a bit.