Gauges fade to black

[DUD2STUD]

I actually have 2 questions on my 72. I recently rebuilt my gauge cluster. Repainted the needles buffed the lens and painted the bezel. There is a black wire with purple stripes that runs from the steering column to the gauges it has a white light socket on the end. I tried turning every thing on and I can't get it to light up. I also replaced the bulb a couple times. I can't remember what it's for or where it is supposed to plug into the gauges. I figured since I can't get it to turn on it must be a warning light but I'm not sure. My other question is I replaced all the bulbs with LEDs. Starting from the upper left near the light switch they are bright but by the time you get to the lower right oil unit they dim to nothing. I have replaced the lower LEDs with the uppers and it doesn't change. I also replaced the turn single lights. The right LED blinker works but the left does not. When I put a standard bulb in the left it works fine. I bench tested all the LEDs and they all work and I also checked the printed circuit board and it looks fine.