When I hook up my lights they won't work until I mount the trailer to the truck. Is that normal?

No. There should be a ground wire in the wiring harness. The coupler makes a poor ground. Check the harness. Usually the white wire. But YMMV. What kind of connector? 4-pin flat. 7-pin round "RV". (Most trucks today come with a 7-pin and/or 4-pin flat.

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The end was cut but he said it was a 4 pin. I wired an end and there is a ground wire mounted to the trailer frame but the lights only work when hooked up? I was told that it is supposed to be that way. the ball completes the ground on the trailer. Also the front side running lights dont work(disconnected due to a short) I hooked those up to the taillight wire and blew the fuse.

You never want to ground with the ball ... you must have a wired ground from the truck to the trailer.

Even better is a ground from the battery - all the way to the trailer lights via wire ... you lights will be MUCH brighter.



Also ball ground will cause your lights to blink on and off as you drive.

I do have a ground on the trailer as well but maybe its not a good connection. If the trailer has a ground to the trailer frame then the lights should work when not attatched to truck right? Maybe my trailer ground is bad?

yep trailer ground is bad. or the truck ground is bad, easy to check