Trailer lights: HELP

Rob Mo.

Member
My trailer has a flat four connection. The plug is founded at the hitch of the trailer & each light is ground @ it's location on the trailer. Problem I have run into is the when the trailer lights are on with any of the blinkers, the light will all flash. I have cleaned all the grounding areas to no change.
 
Sounds like you have a grounding problem between truck and trailer. Trailer not getting proper grounding.
 
i agree with d beatty the first thing to do is ground the truck and trailer to each other normaly this is the white wire on the plug, but for diagnosis, run a separat wire between the truck and trailer, make double sure this wire is securly fastened to bare metal on both the truck frame and trailer frame, then see what it does, and post back we'll take it from there,also make sure those lites have a good bare metal ground on the trailer, more time and money has been spent chasing trailer electrical problems resulting from a bad ground than all other reasons combined
 
I took the light boxes off the trailers & white ground wire on the hitch off & used some 80-grit to shine up those spots. Still the same problem. If this problem can not be corrected, I am going to run a separate ground wire from the plug to each light on the trailer. So the ground will be at the truck. The only other option I have not tried is to take some sand paper & scratch the hitch ball up & maybe the ground will get to the truck. Odd that I have had this trailer for 12 years & never had a probl with it till now.
 
Take a look at the bulbs. Make sure they are seated properly in the socket. If one is not lined up properly with the contacts, it can short the contacts together feeding turn/brake to the running light circuit.

A lamp with a broken element can do the same, fall down and short the two circuits together. So can a lamp that has come unglued from the base and twisted the leads together.

One other test, unplug the trailer and test the pigtail from the truck with a test light. Be sure the proper signal is getting to the trailer. Vehicles with separate turn/brake lights have circuitry to bring the two back together for the trailer lights.

Also check the wiring harnesses of both the vehicle and the trailer. They get smashed, burned and chewed... Anything is possible.
 
i had about the same trouble i ran a wire from the ground side of the battery to the ground side of the plug it fix my problem
 
I too agree with the others sugesting ground problems between truck and trailer with blinking lamp issues..
 
see the white wire in the plug ? that is your ground wire not the hitch ball on the truck side ground the white wire to frame/on trailer side ground white to frame you will have lights
 
Well guys I tell you what. After taking a test light to the truck end of the connection, the problem was in my trailer. I opted to run the trailer down the hwy to that pull last night. Before leaving the venue, I checked my trailer lights and they were working fine. grrrr. As aggravated as I was working on the lights for nearly 2 hours Thursday night, I am still baffled as to what the problem was. I will tell you one thing, I hate working on anything that I can"t physically see, electric is one of them. Thanks for all ya"lls help.
 
Was the ground WIRE from the truck making a good connection? Ive fought those issues before only to have the plug itself be bad on the inside.
 
As the others said it's a ground issue. Now go get those sealed lights like on semi trailers. The regular ones are only about 4-5 dollars each. Put them on with the pigtail that goes with them. Then you can get plug together harness for the trailer run that up to the hitch. Then solder a ground wire from the white ground wire for the ground or if you look for the better harness it will have the ground already in the harness. It will save you time and trouble. The lights will out last the junk plastic box lights you all buy for the cheap program with the 1157 bulb. They have stop,turn and tail in each one of the sealed lights. They also make them in small round or oval style to use for the side marker lights. Best thing since sliced bread for lights.
 
I fought similar problems off and on for some time. Finally found the factory plug on TOW VEHICLE actually was an adapter, and where it connected to tow vehicle wiring harness was corroded - ground connection only! GRRRR!
 
I have had this happen on the road at night. I just used jumper cables from the trailer to the hitch frame on the truck. After you pull it a while sometimes will heal. I have found electric cleaner spray to work.
 
My recommendation for trailer lights to make them reliable is spend the money for LED lights, then with all new wire, solder and heat shrink all connections to keep water out of your new wire. Even if you still use regular bulbs, just soldering and sealing all splices makes a huge difference.
 
Put some dielectric grease in the connector. That solved all the light issues the one hopper was having when we were getting ready for wheat.
Didn't help the other any.
 

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