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.

[GASoline71]

Not sure about the LED's...

...but that black wire with the purple stripe with the light on the end could be the high beam indicator lamp.

Gary

[DUD2STUD]

I tried that it didn't come on

[ray_mcavoy]

I believe that black/purple "wire" leading into the steering column is a fiber optic line to illuminate the auto trans shift indicator. So the white socket on the end needs to be inserted into one of the cluster illumination locations. It should receive power to light the bulb through the printed circuit on the back of the cluster.

As for the other issues, have you checked the voltage at all of the bulbs/sockets? Even though the printed circuit looks good, you might still have a weak connection somewhere causing a voltage drop.

Also try bench testing the bulbs or LEDs in the sockets like this:


I've come across many cases where the bulbs don't always make a good connection with the contacts inside the sockets. The connection is often intermittent (will work if you wiggle the bulb or start to pull it back out of the socket). The fix is to carefully bend the contacts inside the socket and/or the little wire contacts at the base of the bulb for a tighter fit. Also check to make sure the contacts on the sockets are making a good connection with the printed circuit when they're snapped into place.

[Sklptrljay]

That is your fiber optic cable as stated above. If you're looking at the cluster from the back it attaches right of center, basically beside the Tach location.

I believe led's require the use of a special relay because they draw so little wattage.

[DUD2STUD]

Thanks for the help