88 gmc 1500 sierra tail light trouble

[1980 gold]

my friends truck but i'm trying to help. it's an electrical question so here goes. p/s rear blinker and brakelight don't work. tail lights both work fine. new bulbs new flasher hazards work. if you put on the left turn signal both left and right rear blinkers flash. i cleaned up the chassis ground and added a washer the ground is connected to both tailights and license plate lamp harness. should they be grounded indivdually? although they worked before like this. only the left rear brake light works BUT if i switch the tailight circuit boards ( plug the rt one into the left harness and vice versa) the p/s blinker will now work and the brake lights will now work on the right side can i assume that is the circuit board? sorry if anyone got a headache from reading this

[Captkaos]

Check the front bulbs.

[1980 gold]

thanks we'll do one correction when you use the left blinker all 4 blinkers go on (front and rear)

[1980 gold]

ok so i got all 4 to come off at once its weird i pulled all 4 front bulbs put them back i have front and rear d/s blinkers and just front p/s blinkers still no p/s rear blinker or brake light. circuit board?  oh also when i turn on the headlights i lose the d/s front blinker

[Captkaos]

Wait, your talking about a 88 C/K truck...

[1980 gold]

yes

[zieg85]

I had a similar experience with a 1995 C1500 where the problem seemed to move around.  What I did was to take apart the rear lighting and cleaning/greasing back the connections which were intermittent.  The connections were arcing at times, I found the problem at night by accident.

[1980 gold]

hey thanks what it ended up being was the rear bulbs are mountedin their socket in what looks like a printed circuit sandwiched between  layers of plastic i switched the left one that was working to the right side and it worked for both signal and blinker on that side so we ordered one as our salvage yards on long island almost never have anything below 95

[1980 gold]

so we put in rt side circuit board everything works now blinkers brake lights tail lights and i know what to do on next job