I’m in the process of restoring the under dash items on my car. Today i replaced the printed circuit board with a repro and the voltage regulator that mounts to the back of the cluster. It looks like my gages are working now but no lights. Any ideas are appreciated, here’s what I’ve tried
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tested every bulb on the bench and they all worked.
I tested the instrument plug, and on the red and blue wire it showed voltage when I turned it on. It also varies when I turn the rheostat on the light switch. When I plug it in, the lights don’t come on. Tells me I’m getting power to the board
3 only my left blinker and my high beam indicator light comes on when plugged in
4 changed out the instrument fuse, although the old one looks fine
5 I did notice my clock lights were coming on and dimming with the rheostat
6 the light in the ignition switch only comes on why the key is on the accessory position.
7 made sure all connections on the circuit board were solid.
These lights were not working before I did all this either, was hoping this would fix it
Not sure where to go from here. It doesn’t seem like it should be this hard!!
check your grounds as well on the circuit board. I’ve seen a 69 (new) with a sliced open trace on the ground circuit that was hard to see.
You can unplug your circuit card plug and test the blue/red wire for 12V (or less) and see if you’re getting power to the plug. Then test resistance between chassis and the two black wires (ground—typically two black wires, but sometimes one): you should see 1 ohm or less. If both check out, then the problem is either at the circuit card or the plug itself. If either checks bad, the problem is in your wiring.
Most common issue I run into is corrosion in the fuse holder. Often have to use a dremel with a small stone to clean enough corrosion off to complete the circuit. Assemble with Vaseline on the metal fuse end caps to prevent future corrosion.
Thanks. When I checked voltage, I checked from the blue/red wire to the black wire on the plug. Read between 10 and 8v roughly depending on where the rheostat was.
What connection on the circuit board is the ground? Isn’t it part of the wiring in the plug? Black wires?
Make sure that you are getting the connector to the back of the cluster plugged in good. If it isn’t plugged in all the way, things tend to behave abnormally.
Avoid measuring resistance between different colored wires. In this case, you can get low resistance due to the presence of bulbs in the circuit. When measuring resistance, always measure between points of the same circuit or wire color.
Ok, so I looked at the fuse holder for the instrument fuse and cleaned it even though it looked pretty good. I tested the fuse holder without a fuse and I get voltage on the left side of the fuse holder when I pull the light switch. Voltage turns on and off with the switch.
Now I install the fuse. Same test, and I get no voltage on the fuse holder on the left hand side where I had it without the fuse installed or the right hand side of the fuse holder. The fuse is not blown. Took the fuse back out and I get voltage again.
I took the fuse block loose to see if it looked like anything was missing or broken but it looks good.
If something was grounding out wouldn’t the fuse blow?
How is this possible? Why would the voltage to the fuse holder disappear when I install the fuse? I repeated this test at least a half dozen times . Any thoughts?
Depends on how you tested it. If you probed the fuse clips with fuse in, you should get same result. If you probed the fuse itself and got no voltage, that says the fuse is not solidly installed in the clips. I find the clips need to be very tight against the fuse itself. Take a needlenose plier and squeeze the two fuse clips together (obviously without the fuse installed) and then install the fuse. Removing a fuse should be difficult, and often times you’ll end up breaking the glass. That’s a sign of good, solid connections of the fuse to the fuse clip.
In cases like this it is often useful to use a 12 volt lamp instead of a meter as a test load. That way you eliminate cases where you seemingly have continuity but it fails when in use.
Good point, may be losing continuity under load. I bought a test light and will try it tonight. If that is the case I guess I’m looking for a loose wire or connection?
Well, after a lot more testing and headscratching, I finally got it working. I found a few things, I had a loose connection on the switch plug, and I found the ground wire for the printed circuit had broken at some point when I mounted the dash. That was a battle!My hands look like they were chewed by a raccoon with all that metal to work around lol
Now onto the next issues:
I notice the light on the ignition switch only stays on when in the accessories position, should it be on at all times when the lights are on?
The clock light dims with the switch, but never turns off, it stays lit all the time.
