Trailer wiring ???

[FED 387]

Bought a used enclosed trailer---all the lights work HOWEVER when you turn on the flashers or turn signals not only do the taillights work on the trailer although not real brite BUT the clearance lights on the trailer all flash and the Stop lite on the cab flashes too---BOTH turn lites on the truck flash but depending whether you are signaling left or right whichever way you signal that lite will be brighter than the other taillite but both are flashing---Disconnect the trailer and the truck is OK--put a new 7 prong plug on the trailer cuz the old one was a little scuzzy that did not help--- The guy I bought the trailler from had just installed ALL NEW Led clearance lites and 2 NEW regular (not LED)stop/turn lites---Anybody got any ideas??? I think I have a pinched wire some where but do not want to tear the whole interior out to find it---He also put new wood on the ramp door but I have no idea if he rewired it while he had that open- Suggestions gratefully accepted--Thanx Comp 387

[art leong]

I had a problem similar to that. They had one of the brake lights wired to the running lights.
When you put on the lights the brakes locked up.
Trailer wiring on trailers built up north can be a real problem to get to, because they are all enclosed.

[krugracing12]

Add a ground wire from the truck frame to the trailer frame and the trailer frame to rear door frame. We have several older haulmarks that had the same problem and that cured it.

Bill

[FED 387]

OK guys Thanx will look into both ideas---anybody else got any more ideas??? Thanx FED387

[magnumv8]

We do these everyday at the shop so if you haven't solved it yet......if your truck has factory trailer wiring you should be fine there.....if the trailer still has the industry standard color coded cable (wiring) the trailer plug on the trailer gets wired like this with a 7 blade connector....to make it easy ignore the colors printed on the plug and socket and go only by the blade numbers (very small).....

#1....white...10ga wire...ground
#2....blue....12ga wire....trailer brakes
#3....brown....14ga wire.....tail lights,license plate light,marker lights
#4....orange or red....10ga wire....battery charge wire
#5....yellow......14ga wire.......left stop,turn signal
#6....green.....14ga wire.......right stop,turn signal.....
#7.....aux....can be used for whatever,leave empty

if everything is cool from there you said that the previous owner replaced the tail lights (stop/turns)......after double checking everything so far and the ground connection on the trailer frame here is what I would check next.....

The stop/turn light pigtails are 3 wires...one white(ground wire) one black(marker light wire) and one red(stop/turn).....if the previous owner replaced this pigtail it sounds like this is where the problem may be....it sounds like he has the marker light of the pigtail connected to the stop/turn on the trailer wiring,this explains why your trailer tailights blink dim and the marker lights blink also when you put on your turn signals....this would also give a feed back through the trailer plug into the truck causing it to do some strange things too.....


let us know what you find out.....

D L Rambo

[Wayne Ewing]

Sounds to me like you could have a bad ground and some wires crossed up in your plug. Had some of the same problems on my Goldrush this summer and spent 2 days trying to figure it out. Are your trailer wires color coded? If I remember corectly the yellow is left turn, the green is right turn the black is taillights, the white is ground the brown is running lights, the red is to charge the trailer battery and the blue is the trailer lbrakes. The ground wire (white) has to go into the center post of the plug. Hope this helps some.

[FED 387]

Wayne just double checked the wiring on the PLUG---the colored wires are where they are supposed to be---the center wire position on the trailer plug has no wire attached to it --never did days its for backup lites-no wire in the harness is available to attach to it---I do not understand how you run a ground wire from the truck to the trailer when I think going thru the hitch ball would work but if that is not the case how do you ground the trailer to the truck or the trailer door to the trailer frame???( hinges on the trailer door metal on metal not a good enough ground???)---I'm game talk to me this is exasperating spent all day Sun futzing with this bout ready to completely rewire the frigging trailer get it over with BUT I dont wanna do that hafta pull the ceiling down etc.--- Keep those ideas coming ---Comp 387

[Michael Pliska]

Just try temporarily hooking a jumper cable from the truck frame to the trailer frame, to see if grounding is the issue.

[GTX JOHN]

I agree... sounds like a ground wire problem for sure. The LEDS
are not as fussy as conventional bulbs. When the ground is bad my trailer do a lot of backfeeding and funny stuff.

[Greg Reimer 7376]

In about 1973,I worked for a gas station that had U-Haul rental trailers and trucks.You never saw junk until you saw their stuff. People used to rent a trailer, a clamp on bumper hitch, and wonder why the lights misbehaved. That was when bumpers had those big gas shocks suspending them, and continuity of ground wasn't too good to depend on. An auto electrician good enough to quickly diagnose and repair these issues that trailer lights can cause was enough of a rocket scientist that he didn't need to work there. Feed back through defective bulbs, sockets, and grounds would turn a saint into a drinking man. The suggestion to make sure all bulbs are correct for the socket is a good place to start. It might be necessary to remove all bulbs in the trailer, then re-install them one at a time until the glitch reappears. Good luck- it's probably something simple.