A new issue with my '72 Super... and I need some new ideas! I'm a bad electrician, so I'm muddling my way through with old posts on similar problems. But I'm out of material.
The gauge lights have functioned normally the entire time I've had this truck, with the exception of two occasions where the following problem showed up for a few seconds, then went away immediately. But the other day I drove home in the dark, and the problem appeared and hasn't gone away. So, I've gotta figure it out.
When the parking lights or headlights are turned on, all the gauge lights come on, but dimmer than normal. The turn signal indicators come on steady; the high beam indicator comes on steady; and when the turn signals are activated, the opposite indicator flashes along with half the dashboard.
I figured it was a grounding issue. So, I crawled under there and took a look at things. It's a tach panel, and the printed circuit is a newer replacement. Everything looks nice and tidy, maybe not factory, but not a rat's nest of splices. The cluster plug appears to have all the right colors in the right places. All the gauges and bulbs work. The factory ground clip on the dash is in place. All the factory printed circuit ground screws are tight (I loosened and tightened them all just to make sure they were getting good contact). Just for kicks, I ran a ground wire from various screws on the printed circuit and panel to the brake pedal bracket, trying the lights after each arrangement. No change.
Then, I thought maybe the cab wasn't grounding to the frame well enough. So, I ran a wire from cab to frame while trying various things under the dash. No dice!
Finally, I decided to check all the exterior light bulbs, although everything works normally - headlights, taillights, turn signals, reverse lights, brake lights, even the side indicators. I pulled all the lenses and checked to make sure the dual-filament bulbs didn't have a single burnt filament that was shorting the other one. Nope.
Another guy on the forum had the exact same symptoms recently, but he just needed to tighten a loose printed circuit ground screw. Now I'm just confused, and have no idea what to try next. Any electrical superstars out there?
Finally, since people like pictures, here's a little motivation to get those creative ideas flowing: