Turn on my right turn signal and brake lights flash instead

[Scott Haggard]

I've got 2003 gmc Sierra 2500hd. When I turn my right turn signal on bulb lights up but doesn't flash. It's also causes both brake lights to come on and both of them will start flashing.  It's just the right side that does it but it's an intermitten problem. I'm thinking it's in my multifunction switch but not 100% sure. Has anyone else had this issue before? Any help is greatly appreciated 

[silveradosid]

you have a ground problem with probably the right rear light, take it out and check the wiring

[Scott Haggard]

OK I've checked the wiring at the right rear tail light I've even checked the left tail light wiring and the junction box that they plug into and everything looks good. Any other ideas? Is there a ground wire ran to the frame in the rear of the truck?

[Big_kid]

I agree. Ground issue. It’s using the other bulbs ground, that’s why that bulb is lighting up also…

[Scott Haggard]

OK I understand that. Does anyone know where the ground for the taillights is at on the frame?

[Scott Haggard]

Still needing some input from someone on where all the grounds are located. I've found one on the frame horn on the driver's side, one under cab on driver side, on back of the motor, and one on the back side of the gas cap 

[Supreme Pizza]

I have seen some VERY strange behavior from tail/brake lights under the following conditions:

 

Incorrect bulb installed in tail or brake light socket.

 

A single terminal bulb installed in a dual terminal socket can cross power between the circuits and things go haywire.

 

Is this the problem on your rig? Who knows. Might be worth a look though.