Blinkers Alternate w/lights on

[brocsbar]

I got a 2007 GMC Sierra 5.3 Vin Z with a electrical blinker/light problem. Works fine in the rear but in the front have the problem. With no headlights on the front, the front blinkers work normal but when the lights are on and the left blinker is on the 2 left blinkers in the front alternate and the same when the right blinkers are on with the lights ---they alternate between themselves. By alternate i mean the two bulbs on the SAME side (in the front) flash at different times. But Don't when the headlights are off, then they both blink together as they should. The rear lights on the truck aren't affected but the MAIN problem is that I pull a trailer and when it is hooked up to the trailer and I have on EITHER blinker they both alternately blink in the rear (but not on the truck)

[brocsbar]

Nobody? I've tried to look at the DRL's but they aren't a factor. (they don't work on their own but when I supply ground to the relay under the hood they work) but it doesn't change the way the blinkers react. Light Switch?? Any and all insight is very appreciated.

[gmtech1]

Does this have a factory trailer harness/trailer brake set up?

[brocsbar]

Yes it does. I've checked out that both his trailers are wired right

[gmtech1]

Checked the bulbs? They can do funny things when they have problems.

[brocsbar]

Yup checked all bulbs and sockets

[brocsbar]

I'm changing the headlight switch tonight and will let you know