73-87 Chevy _ GMC Trucks > Instrumentation

Turn Signal Indicators Not Working In Dash

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Localbulldog:
1986 K20 Custom Deluxe
I replaced the printed circuit board today, cleaned sockets, new bulbs and new gauge clips.  I have one bulb not working that back lights the gauges which is located just above the wiring harness plug.  I've swapped out the bulb with other known working bulbs and its still not working. I have turn signals and 4 way flashers outside the truck and can hear the flashers for both but the turn signal indicators do not come on at the dash which I've also swapped out the bulbs with other working bulbs and its still not working.

All the lights worked prior to replacing the printed circuit board with the exception of the brake light which after removal was torn.

Any help would be appreciated, thank you!

bd:
Compare the new PCB to the old PCB.  Make sure the circuit foil routings are identical.  Also, make sure that none of the foils are severed by an incorrectly broached hole through the new PCB.  If the PCB passes visual inspection, use an incandescent test light to verify power and ground to each bulb that doesn't illuminate.

Localbulldog:
Thank you! The two look the same with no breaks.  How do I run that test?

Localbulldog:
I put the old PCB back in and everything works with the exception of the brake light!  Bad PCB I guess ...

bd:
Verify a good ground point for the test light by clipping the test light to the proposed ground and probing a known B+ source in the fuse box.  If the test light illuminates, the test light ground is valid.

To verify power to the bulb socket, switch power to the bulb circuit ON and probe the socket terminals.  If the test light illuminates, the bulb socket is receiving power.  Note that only one socket terminal should illuminate the test light.  If both socket terminals illuminate the test light, either the bulb ground is open or power is being delivered to both sides of the bulb socket.  To determine which is the case, remove the bulb and probe both socket foils on the PCB.  Only one foil should be energized.

To verify ground to the bulb socket, clip the test light to the B+ source used earlier and probe the opposing bulb socket terminal.  If the test light illuminates, the bulb ground has been verified and the issue is with the bulb, its socket, or socket connections.  If the test light does not illuminate, there is a ground fault.

More than likely the problem is with the new PCB.  Are the foil contact points for the sockets and the IP harness connector bare copper, clean and bright?  You can use a soft pencil eraser to burnish them if needed, but be careful not to dislodge the foils from the PCB substrate.

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