I have a 85 Chevy truck and blinkers don't work in the back but when I turn the right signal both start to flash?

Have you had any wiring worked on or trailer wiring added?

No I haven't I just got the truck

I would remove the light bulbs and test each socket for blinker pulse. If no + blinker pulse then inspect blinker relay. Also check that each socket ohms out a good ground. (- negative connection) if no good ground then back track wires for a good ground or in some cases can add a frame ground close by and tie it into socket. Inspect each socket for corrosion (light green film over bulb and socket connections). Also check to make sure it has the proper bulbs in it. Use bulb lube when reinstalling bulbs. With both blinking when right turn is on I would start with right bulb first. If they are dual element bulbs it could be back feeding the left bulb on the parking lights element.

Ok thank you very much guys very useful tips...Aloha

Srry dandyoun I meant to like all of your guys answer ill get back with the results tomorrow

I know that when I got my 91 Chevy I had similar issues with no brake lights or reverse lights and both signals flashed when I tested the turn signals. The issue in my case was that the previous owner ripped the wires during a off road excursion then decided to try and fix it well enough to sell me the truck. It took me 3 hrs to trace the wires and fix the problem. You might want to try this as it is very common issue now. Best bet is your signal wires are connected to the same quite causing this issue. I hope this helps.

Sorry same wire not quite

I agree with demontoad. That's where I was going with my question.

At times one bulb is burnt out causing the above described problem. Make sure the bulbs are operational before getting under the truck to chase bad or corroded wires. Always do the easier fix first, it usually is the cheapest also. Mr. Roy is right with the ground getting bad, and dandyoun is correct with checking the sockets and ground wiring.

As with Marks answer most likely problem is poor or missing ground. If bulbs and ground are ok then ck flasher itself and lastly unit in colum. Gm didn't make better switches till the 90"s.

I too have a 1985 GM truck. I too was having issues with the turn signals working. My flash covers on both the front and sides were cracked. I replaced those, then I found that both the sockets had damage on the inside. I replaced them both, and for the most part they work great. The only thing I have a question about is this: when the headlights are off, they work perfectly, but when the headlights are on, each side will flash alternately with it's side's marker. So for instance, if the left side marker flashes on, the front left flashes off, and vice versa. Probably still a grounding issue???

On GM vehicles, by design they flash alternately with the parking lights on as the side markers do not have a true ground but 2 hot wires

Thank you.

What he said.