When i put the left signal the front light flahes. When i put right signal the hazard lights go on. Ive replaced signal switch, light bulbs, relays, fuses, even bulb boards. What culd it be.

Asked by Jan 27, 2015 at 04:00 PM about the 1988 GMC Sierra

Question type: Maintenance & Repair

3 Answers


Possibly a bad connection or ground at one of the bulb sockets. Also might be the turn signal switch.


You need a schematic for that rig in that year with that specific type light arrangement. I foud them at autozone website. You may have to print several and tape them together legibly, then tack it to the wall. You would be concerned with the plug and schematic for the turn sig sw., the hazard sw. and the flashers. only you , know what specifically has been done to it, now you have to trace and test to find it. Are the parts plugged in exactly right ? are the wires different on one plug for some reason? who knows. Napa sells some of those harnesses and light parts and way cheaper than GM. but they may not be perfect. patience and perseverence my friend.


The stuff you would have already done must have included inspection of every bulb and ground for crossed filament trouble in bulbs with multiple filaments. Also you found socket trouble, and went for the printed circuit boards, but if you are wired for towing anything, it can be that the wires and connections with those come into play. I had a truck in the shop years ago like that where the wires were changed around compared to the part we were installing. we had to search the map.

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