Odd I/P Electrical concern - Videos attached

Has anyone seen this concern before? Please see Youtube links below.

Before I go poking and prodding in near 50 year old wire, I thought I'd ask if anyone has seen this concern before.

Note:
All EXTERIOR electrical lighting works properly under ALL conditions.

Dimmer switch only allows full I/P backlighting or no I/P backlighting. Also the dome light feature is inoperative. The switch has operated this way for years. The concern in the videos is new.

Suspecting:
Faulty electrical switch
Poor ground
Shorted wiring/connector/component/Instrument Panel

https://youtu.be/CO2scHN8d5o

https://youtu.be/N0XcM3lz-FM

Bad Ground(s) for sure.

Check them all both at the turn signals and most definitely at the cluster. The symptom of your fuel gauge, and also likely temp gauge pegging like that with the lights on is a sure sign of a bad ground. Your cluster is finding ground through the senders and/or turn indicators.

Bet you've either got a broken pin on the circuit board or just simply a poor or corroded ground somewhere. It never hurts to add a secondary ground wire simply because you can't trust 50 year old wiring.

Do you know where the I/P or body harness grounds are located on a 1969 Plymouth B-Body?

I do not.

What I would do to start is simply create a healthy length of wire, and connect it to ground on your cluster and a solid, clean area somewhere under the dash. I would almost guarantee these symptoms will go away.

Gremlins. You might be able to find a gremlin trap at your local animal control office.

I'd start with the wiring diagram. Make a paper or scanned copy and trace in the wire colors for everything that's effected/not working right. Then make a simplified version (or digitally erase the rest). Take each item back to its power source. It will either be fused or through the headlight circuit breaker.

Then you can figure out what should be hot (on). Since some things are hot when they shouldn't be, you can then figure out where (which wires/switches) they may be getting power from. Then you'll know where to look.

X2

Do not forget to check the ground on the dimmer / dome light switch

I chased a bad ground causing turn signal indicators to light when they were not on. Found it on the drivers side on the socket itself for the front lamp.

I had a friend in High School that had a '69 Fury Convertible. Very rusty car. If you turned the hazard flashers on, the two-segment tail lights looked like wig-wags. That's where I first learned about ground issues

denfireguy raises an excellent point. Could be faulty grounds at the socket, too. Make sure everything is clean. Also double check to make sure your bulbs are the correct type. Cramming a single-pole lamp into a double-pole socket can also create weirdness.

X3 When an electrical issue seems too goofy and nothing makes sense, it's a ground issue.

Hello All,

Just wanted to report back that the issue was/is defiantly ground related.

I used one of my jumper leads and installed it from the ground tab on the cluster voltage regulator to a good ground under the dash. Concern was eliminated. I will try to locate the source of the faulty ground, but applying a good ground did solve the issue. I will also install a new permit ground under the dash.

Thanks to all for your input, especially RamblerMan!

The instrument cluster grounds through the screws that hold it to the dash. It never hurts to add a ground anyway.