Diagnosing 68 912 Dash Gauge Backlighting Issues

[5horizonsrr]

Hi everyone, I hope you are all safe and healthy

I'd appreciate a little assistance with diagnosing a problem in my 1968 912. The other day I had the car out later than usual, as the grocery stores here are seemingly only calm late at night. I noticed the backlighting on two of my gauges (fuel gauge on left and the temp gauge next to it) was out, no light on the fuel gauge and dim lighting (one bulb out) on the temp gauge.

Anyhow, assuming it was the bulbs I went to swap them out, and was surprised to find the bulbs were ok. I "pulled and rejoined" the contacts and similar visual checks, but it would appear (voltmeter confirmed) they aren't getting any power at the spades. This is especially odd for two reasons:

1- other lights on the daisy chain of a circuit (blue & yellow wire) are lighting up
2- the indicator/alert lights on the same gauges seem to be working

I pulled one socket out entirely (vs just the bulb itself) to confirm they aren't the problem, and no luck. When removed from the car on a test transformer the whole assembly (bulb + socket) worked, so it is in the wiring somewhere

A visual check of the fusebox and the extra fuse on the green/white wire all seem fine.

Might anyone have a guess as to what I can check or do? Happy to snap images or check anything, I'm "sheltering at home" so time is on my side!

[WFBowen]

Some pics would help. You probably did this, but double check that each gauge is properly grounded.
Bill

[5horizonsrr]

Hi, an update after more investigation:

So one problem can be checked off the list: the temp gauge light was actually the third bulb for the oil pressure lamp- and supposed to be off when parked in the garage. User error...

Back to the fuel gauge, it only has one lamp- which I presume to be for the red "low fuel" warning. Is this gauge even supposed to be backlit at all? An image of the bulb is below.

And a related question- is the main light/headlight switch actually supposed to dim when you twist it? That could be my problem- it does nothing and may be stuck on a low(ish) voltage of the rheostat.

And the last lighting question: the last image below is of a light "hanging out" by my fusebox- any idea if that is supposed to be there? its not working either, but then again maybe it isn't supposed to be.

Thanks in advance!