Brake light out and both turn signal lights blink

[Rough_Fish]

Just get one problem taken care of and now I have another. When hooked up to my 2005 GMC 1/2 Ton Sierra, my right Shoreland'r trailer brake light is out. Bulb is good, but I tried a new one anyway. Also, the right signal light works fine, but when I put on left turn signal, both right and left blink. I have traced it back to the truck by testing the plug coming out of the back of my truck. It tests out exactly as the problem I described. Harness is factory. I have checked fuses in the cab and under the hood . . . all good. I also flipped flopped the wiring on the trailer from left to the right just to make sure it wasn't the wiring going back to the tail lights, but right side worked just fine when I did this and then the left mimicked what the right had been doing. Seems like a strange problem and I am now stumped. I read on the net about some kind of control modules, but not sure if I have one or where it might be located. It is not in the the fuse box on the left side panel of the steering wheel or under the dash beneath the steering wheel. Anyone have any ideas?

[SilverSog]

I have a 2003 SIlverado and had the same problem. Believe it or not the culprit was the turn signal flasher. I know that seems strange when your problem is with the brake lights. I always assumed that if my trailer's turn lights flashed then the brake lights would be fine too. Logic: They're the same connector on the truck, right? Now I always test the brake lights AND the turn signals!

Good luck! I know your frustration.

[heat checker]

Mine was doing some real funky stuff last year. Turned out it was a bad ground. Ground the trailer to pickup with battery cables just to rule out.

[graphicpunk]

I just rewired my trailer and it did the same thing. Both blinkers worked just fine but the breaks didn't like up one bit. I just undid where my wires were spliced and made sure the ground was tight against the metal and it worked. The main problem with my trailer is it is a two piece break away trailer so it didn't ground that well in the second half. I took a grinder tool and ground down all the old paint, and rust and took it to bare metal. Basically it is your ground that isn't working. Just make sure its tight to the metal and if you have a two piece trailer I would suggest cleaning up the area where the two pieces connect. Also you can buy a little four prong tester deal, at Fleet Farm, that you can plug into your car's output and see if the brake lights and blinkers are working at that point.

Its a lot of frustrating work but keep with it and you will get it to work.

[jeffreyd]

sounds like a ground problem to me. remove connection to ground at light and at tongue. clean all the paint off, replace crimped eyelet where screw goes thru, and recheck. if that is the problem after you get it all together and making sure it is clean, apply some protection to the connections to keep them from rusting. you could also take a test light and check the ground at the light.

[marine_man]

I have traced it back to the truck by testing the plug coming out of the back of my truck. It tests out exactly as the problem I described.

It sounds like the issue is with his tow vehicle guys; not a grounding problem on the trailer (although that is pretty common).

marine_man

[graphicpunk]

I still say its a ground problem unless the tester confirms that the problem exists coming out of the trucks output.

Buy one of these, if you haven't yet, [Note From Admin: Please read forum policy before posting again. Thank you.] and if the left and right blink separately and both come on for the brakes then it is a ground.

[Rough_Fish]

Problem solved. It was the flasher module. Apparently it does more than flash, and I guess it should for $35. I would have never guess it would have been this since my actual truck lights were all working fine, including blinkers. I would have bet the bank it was a ground issue, but 2 hours later after re-wiring the trailer, I was still with the same problem and pretty po'd. Trailer wiring can be really frustrating. SilverSog nabbed it. Thanks for the help.

[graphicpunk]

well good thing you found it. My trailer was all rusted out and junk so I tried everything over and over again and I could never get it to work. Eventually it just worked and I think it was a faulty ground but man I think I have wasted a total of 12 hours on re-wiring my trailer. Sad part is it isn't that complicated as for the wiring part goes. It's the making it work right that is the pain in the [PoorWordUsage].