Well, I have replaced the instrument panel lights with LED's on my 2002 XJR, but somehow I have created another problem, far worse than having some dark gauges.
After returning the instrument cluster to its place and plugging back in those two difficult multi-pins connectors, then turning on the ignition, I have error messages galore on the message center:

1. "Engine coolant low"
2. "Low oil pressure"
3. "Battery not charging"

Each one of those messages are also announced with a red lit symbol, or in the case of fuel indication, with a lit ("low fuel") orange dot.
The coolant temp gauge and the fuel gauge are both inoperative, but the RPM gauge works; still need to drive the car to confirm the speedometer.
I have charged the battery to almost 13 volts, but it hasn't made a difference.

The instrument panel schematic diagram shows the three affected gauges inputs to the instrument panel as 3 totally separate inputs with nothing common between them, so it'll be difficult to blame the quality of their signals individual inputs to the gauges as bad and causing the errors displays; can't be three bad inputs, so it would have to be inside the instruments cluster? Was it my work removing and installing the instrument panel from the car that triggered something bad? Am I in for a replacement cluster? I can't think that light bulbs can cause anything like this as they're in a totally different function/circuit. - Then, to add insult to injury, the far right instruments light is still out with a known good bulb and a correct LED polarity confirmed with my 12 volt power supply, meaning that the instrument lights still need more work.... Yeah, here, go ahead and slap my other cheek....

Anybody with a like previous experience? Tips are most welcome.

Thanks and regards

 

Most probably, you did not plug one of the connectors fully in.

 

I agree one or both plugs are not correctly seated. Open it back up and make sure to seat the plug firmly before moving the latch in place.

 

Oh, man, you guys are kind of giving me the hope I've been longing for...
Thank you, both you guys, never thought of that. I'll do that first thing in the morning.

Cheers

 

TSBs for you.

bob