Everything works except with the park lights on and i step on the brake pedal, lights go out on trailer let off and they come back on. With the parking lights off they work normal.

Check all the grounds. Seems like majority of trailer light problems are related to poor ground - especially odd ones like you describe.

Dittos on HB's diagnosis... Have had several trailer light problems with the golfcart hauler... grounds has to be pristeenly clean, and tight!

Well thought i redid the ground, shouldn't be any grounds in the back should there? There was a wire on the front of the trailer that went from the plug to a bolt on the trailer I assumed this was the ground but when i unhooked it from the bolt i still had the same problem, and the lights were still working.

You probably were getting ground through hitch ball when you disconnect that wire. Since your plug's ground wire "grounds" to the trailer frame, that would indicate that each light grounds to the trailer frame also. Check each light for a similar wire that is bolted/screwed to the trailer frame. Dunking at the ramp may have corroded it.

As others have said, the ground is very important. Strange things happen without it.

Also do your wires run inside the trailer frame? If they do, they may have wiggled and jiggled inside the rail enough to wear the insulation off and are shorting out.

I once drove a semi that had that problem, and the lights did all sorts of wacky things.

Even if they are not inside the frame,check them every place where they touch the frame, penetrate the frame, etc.

Most of the trailer lights i've seen ground through the mount bolt.

Also if your truck hitch was wired by U-Haul, make sure they actually connected the ground! I took my left taillamp out last week to see the white wire just cut off, less than 1.5 inches from a body screw that had the factory taillamp ground attached to it! Idiots at U-Haul, I tell ya! Hooked the white wire to that ground, and my problems (all lights flashed when turn signal was activated and the brake lights weren't brighter than the tail lights) were gone. Best of luck to you.

Yep, make sure all grounds are good.