Puzzling Trailer Light Problem

[jclaucks]

I have a trailer that came to me with only two rear lights on it. I purchased four(4) clearance lights and another set of brake/turn lights. The trailer lights when wired worked great with my dad's dodge dakota...plenty of blink, etc. On my GMC Jimmy however, one set of the brake/turn lights do not work and the other set blink very slowly...if i detach one set of clearance lights and one set of brake/turn lights the others work great...why would this happen? Why it work great with one truck and not the other? How can I correct the problem?

 

[Ranger354]

Re: Puzzling Trailer Light Problem

Ground.... Ground... Ground.....<br /><br />75% of all trailer light problems are caused by ground wires or the ball and hitch not getting a good conection. Double check all of this. Make sure the clearance light grounds are good also.<br /><br />I used to use stainless balls on all my hitches. I went back to Heavy Carbon steel because they seem to transfer ground better.<br /><br />HOpe this helps. Ranger

 

[chris in va]

Re: Puzzling Trailer Light Problem

Ditto. You can test it by running a ground wire straight from the trailer to the truck somewhere. If it works like that, you have a grounding problem. <br /><br />I had similar issues and thought the truck wiring or trailer lights were faulty, but it was just grounding.

 

[QuadDriver]

Re: Puzzling Trailer Light Problem

Ground problem. On later model chevy/gmcs the rear turn signals ground differently (right turn causes the heater lights to blink, left turn blinks the front marker lights.) goofy aint it?<br /><br />Took me a while to figure this out when I fixed up my 88

 

[SpinnerBait_Nut]

Re: Puzzling Trailer Light Problem

Just make sure all the lights on the trailer is grounded good and then make sure the white wire in the pig tail on the truck is to a good ground and that the white wire on the trailer is to a good ground.

 

[AK_Chappy]

Re: Puzzling Trailer Light Problem

I have had similar problems with towing snowmachine, boat trailers all sorts. The lights would work fine for my truck, turn signals but no brakes when hooked up to my buddies truck, vice versa after hooking back up to my truck again. It all came down to the ground. Ensure the white wire on both connectors goes to a good ground. Take a wire brush or wire wheel on a drill and scrape off the paint down to bare shiny metal put a terminal that a screw or bolt will go through on the wire and connect it to the clean spot. Do this on both the trailer and truck. You can get voltage all the way back to the lights but without a good ground it doesn't do any good. If the lights only have the two wires then yes they are and internal ground. Make sure you also take the wire wheel to the area that the nuts or bolts attach to. Also ensure that they are mounted on a metal bracket attached to the trailer. If not, you can hook up a jumper wire to connect it to the metal part of the trailer.<br />Hope that helps.

 

[Bondo]

Re: Puzzling Trailer Light Problem

Just an Old Indian Trick my Mentor taught me Many Moons Ago.....<br />To Check the Ground, Or to establish ground on a cold rainy night... Use your Jumper Cables..... From your tow-vechicle bumper, or frame, to the trailer frame....<br />Works Everytime.....

 

[dakotashooter2]

Re: Puzzling Trailer Light Problem

It seems that all agree it is a grounding problem. Are you using the plug in type wiring harness that taps into your vehicle existing wiring harness? I found out (from my mechanic)that many of the "after market" harnesses the ground wire is not correct and this leads to some strange problems. I had this experience with my Dakota and it is probably applies for some other vehicles too. It is best to stick with the factory made harnesses (chrysler, ford, GM)even though they cost a bit more.

 

[Ken G]

Re: Puzzling Trailer Light Problem

If all of your grounds are good, and the lights work with the the Dodge the problem is with your GMC. When I first started towing with an '84 S-10 the lights would blink slowly. It was an easy fix. You need to replace the flasher unit on your truck. You can get a replacement heavy duty flasher at any auto parts store. Mine was an aluminum round module that plugged into the fuse panel. Your owners manual should have a diagram of your fuse panel showing the location of the flasher. Its been awhile since I've bought one but they don't cost much.

 

[CatCruzer]

Re: Puzzling Trailer Light Problem

I would check your flasher fuse, to see if it has a heavy duty flasher. I know a standard flasher will make them blink really fast and not that bright. You are not getting enough voltage back to the trailer light with an standard flasher fuse. The flasher fuse is in the fuse panel usally under the left hand side of dash, its the big round looking one. Most of them are made of some sort of metal, and some are plastic. Hope this helps.<br /><br />CatCruzer

 

[lakeman1999]

Re: Puzzling Trailer Light Problem

I would not have thought that anyone depended on hitch to ball for their trailer light grounding. Would you call that soft wiring??

 

[Tacklewasher]

Re: Puzzling Trailer Light Problem

Maybe check the ground.<br /><br />Oh, someone suggested that already.