moonsandals

One backlight in the instrument panel (that lights up the dash when headlights are on, the bulb on the left behind the tach) has not worked since I bought the XJ. A few months after I bought the XJ, I pulled the dash and gauges and fixed any electrical that had issues. I checked this wires going off of the back of the gauge cluster and I am pretty sure it was OK when I checked continuity. The film circuit on the back, that makes contact with the bulb socket, seems a bit worn around this bulb. 'I've looked for replacement circuit films but haven't found anything.
I've changed bulbs (to LEDs), swapped orientation of the bulbs, swapped bulb sockets. No dice.
I'm pretty sure I tried making sure the pins in the harness that plugs into the back of the cluster has positive contact when it plugs in. I could check that and bend the pin out if more contact is needed.
I put a new headlight switch in when I pulled the dash and it did nothing to fix this particular problem.
Up until recently, this bulb never turned on ever. The other dash and interior lights all work perfectly fine.

Recently I changed the headlights to new housings/ bulbs, and put the headlight relay harness in. The first time after this that my wife turned on the headlights for more than 30 seconds this bulb began to flicker and then turned on. Now every time we drive the Jeep this bulb is sometimes on, sometimes off.
My wife has tried twisting the headlight switch left/ right to play with the dimmer to see if that has an effect and it does not.

I'm curious - where should I be looking to get this to light to turn on permanently? I've been half heartedly chasing this for 2 years and I'd like it fixed.
I'm not familiar with this circuit - is there a possibility the addition of the headlight relay is allowing more voltage to the dash lights now (less voltage drop through switch due to headlights)? Am I dealing with some high resistance somewhere in this circuit?

I'm in a 1991 XJ Limited. My build thread has a bit more details on the work done.