Both Trailer Lights Flash

[Rogue86]

I'm having an issue with my 07 Classic Sierra. When I hook up my 4 pin trailer to the GM adapter to go from 7 pin to 4 pin and turn on the left or right turn signal, BOTH trailer lights flash.

 

Grounds are good and all of the fuses are good on the truck. What could cause this? How might I correct it?

 

Thanks

[thearborbarber]

Are the trailer lights bright when this happens or a little dim like driving lights. Sounds like trons are back feeding through the driving light filament which indicated a light socket problem or adapter issue. Hard to accurately troubleshoot without being there.

[Rogue86]

Are the trailer lights bright when this happens or a little dim like driving lights. Sounds like trons are back feeding through the driving light filament which indicated a light socket problem or adapter issue. Hard to accurately troubleshoot without being there.

 

 

They are a little bit dim. I didn't try it with the headlights turned on. Think that might be the cause? (ie turn signals with DRL's only on?)

[thearborbarber]

I think it's backfeeding through the trailer lamps.

[Gregorio]

Unplug the trailer and use a circuit tester on the plug to make sure it isn't the adapter or the truck. However, I expect it will be fine. Like the previous posts say, it is likely a problem with the trailer lights. Either a bulb is screwed in backwards or there is a short at the housing.

[stewy_05]

I think it might be the adapter. Mine does the same thing when I'm towing a trailer and need the 4 pin adapter. My LED tailgate light bar uses the 4 pin also and one side does not get brighter when I hit the brake, but the Light bar is still good.