# electrical question hooking up a trailer **URL:** \ **Category:** Factual Questions\ **Created:** [October 9, 2014, 12:35am UTC](https://boards.straightdope.com/t/electrical-question-hooking-up-a-trailer/700811 "2014-10-09T00:35:43Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![eme](https://avatars.discourse-cdn.com/v4/letter/e/8dc957/32.png) [@eme](https://boards.straightdope.com/u/eme)\ **Post date:** [October 9, 2014, 12:35am UTC](https://boards.straightdope.com/t/electrical-question-hooking-up-a-trailer/700811/1 "2014-10-09T00:35:43Z")
trailer lights rewired and work directly off a battery. PU truck trailer light housing works with test light…When I hook up housing to trailer , trailer lights don’t work… all grounds ok help ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [October 9, 2014, 12:40am UTC](https://boards.straightdope.com/t/electrical-question-hooking-up-a-trailer/700811/2 "2014-10-09T00:40:48Z")
4 or 7 pin trailer connector? Are you certain it was re-wired correctly? ---
**Author:** ![eme](https://avatars.discourse-cdn.com/v4/letter/e/8dc957/32.png) [@eme](https://boards.straightdope.com/u/eme)\ **Post date:** [October 9, 2014, 1:32am UTC](https://boards.straightdope.com/t/electrical-question-hooking-up-a-trailer/700811/3 "2014-10-09T01:32:09Z")
> [@jz78817](#): > > 4 or 7 pin trailer connector? Are you certain it was re-wired correctly? 4 yes rewired correctly ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [October 9, 2014, 3:37am UTC](https://boards.straightdope.com/t/electrical-question-hooking-up-a-trailer/700811/4 "2014-10-09T03:37:20Z")
Are you sure you have a good ground between trailer and truck? Greasy balls are no good in this case either. ---
**Author:** ![HipGnosis](https://avatars.discourse-cdn.com/v4/letter/h/76d3ee/32.png) [@HipGnosis](https://boards.straightdope.com/u/HipGnosis)\ **Post date:** [October 9, 2014, 3:26pm UTC](https://boards.straightdope.com/t/electrical-question-hooking-up-a-trailer/700811/5 "2014-10-09T15:26:29Z")
If none of the lights work, it’s your ground connection as that’s the common factor. ---
**Author:** ![excavating\_for\_a\_mind](https://avatars.discourse-cdn.com/v4/letter/e/e8c25b/32.png) [@excavating\_for\_a\_mind](https://boards.straightdope.com/u/excavating_for_a_mind)\ **Post date:** [October 9, 2014, 3:33pm UTC](https://boards.straightdope.com/t/electrical-question-hooking-up-a-trailer/700811/6 "2014-10-09T15:33:53Z")
The white wire of the connector should be ground. Depending on grounding through the hitch is not reliable. Make sure the white wires of both connectors are connected to a good ground and verify both grounds with the test light. Either that or (one that I have run across several times), the laws of physics change when dealing with trailers. ---
**Author:** ![Gbro](https://avatars.discourse-cdn.com/v4/letter/g/c6cbf5/32.png) [@Gbro](https://boards.straightdope.com/u/Gbro)\ **Post date:** [October 9, 2014, 11:34pm UTC](https://boards.straightdope.com/t/electrical-question-hooking-up-a-trailer/700811/7 "2014-10-09T23:34:27Z")
Yes the grounds are the most common problem. What i do for a first test is to grab my jumper cables and ground the trailer to the truck. Then are the lights on the trailer grounded to the trailer? of course this isnt always necessary when the harness has a ground wire. Are you using a converter of any kind in this wiring?? I have also cut my brand new harness the very 1st time i backed up to trailer when ball hit tongue. I make it a point to run the harness out a grommeted hole in the side of the tongue after that. ---
**Author:** ![Renee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/renee/32/287_2.png) [@Renee](https://boards.straightdope.com/u/Renee)\ **Post date:** [October 10, 2014, 1:56am UTC](https://boards.straightdope.com/t/electrical-question-hooking-up-a-trailer/700811/8 "2014-10-10T01:56:00Z")
Check the fuse in the truck.