Half of dash lights work?!?!?!

[HIGHWAY BY THE SEA]

A while back I decided to install green LEDs into the gauge cluster of my 67 GMC to make the gauges easier to see at night. This worked so well for me that I went and bought more green LEDs to install them into my 68 C10.
I always feel a sense of apprehension whenever I am endeavoring to alter something on one of my trucks that is already in working condition, because it seems that this is when the "gremlins" strike! How does that old military saying go? "If it is not broken do not fix it". I felt no such apprehension doing this to the 67 because I actually used parts I bought from board members to assemble the gauge cluster, so it was not working until I completed the assembly.
But tonight I removed the far left gauge-illumination bulbs from my 68, installed the green LEDs, and they glowed perfectly. But when I got to the right side ones (either side of the fuel gauge) and installed the new ones, NEITHER would illuminate! I removed them several times, bent the connectors upwards, switched the polarity, tried again with filament bulbs, and fiddled with them. NOTHING!!
So for some reason, just because I removed two bulbs from the gauge cluster, now NO bulb will work in those slots but the other side is lit perfectly! Jesus Christ, I HATE electrical gremlins!!!

[rustytruck50]

Maybe a faulty printed circuit is to blame...pretty sure I have the same issue as you

[dmjlambert]

On mine I found it easier to work on the cluster while it was removed from the truck. Removing the cluster is not too hard. You just disconnect the electric connector by squeezing the tabs of it, unscrew the speedometer cable and oil gauge tube, putting a catch pan under the tube, and remove the screws and knobs and nuts that hold the panel on, then maneuver it around to remove it. Some people find they need to loosen and slightly lower the steering column, but on my truck I don't need to do that.

When I have it out and sitting face down on a towel on the workbench, I can supply the appropriate pins on the connector hole with 12V and ground from a lawn mower or UPS battery and test all the lights. I removed all the lights and cleaned up the metal of the printed circuit and the metal tabs on the bulb holders with some brass-o tarnish remover on a q-tip and got them nice and clean. Also cleaned the printed circuit at the connector. The bulbs work better now. Repeat every 50 years as needed.

Here is the diagram for troubleshooting. http://67-72chevytrucks.com/vboard/s...d.php?t=709847

[rustytruck50]

Originally Posted by dmjlambert

Repeat every 50 years as needed.
http://67-72chevytrucks.com/vboard/s...d.php?t=709847

I liked that alot
If only more maintenance was like that

[Willys_MB]

I had a similar issue. I went back there to fiddle around and just by moving things around I got all of the lights to work, except for the one that I really wanted to get working. Either way, it could just be corroded contacts. I plan on taking it out when I do a new wiring harness and cleaning it up and putting in the LED bulbs. They make some that just plug right in and they're super bright.