I'm using a GM harness in my F100 and last night I was ops checking everything and I noticed there doesn't seem to be a lot of adjustability in the dash light dimmer function of my GM light switch.
I'm using Autometer gages. There doesn't appear to be anything physically wrong with the rheostat in the switch, but the gage lights are either on or off, no in between.
Would it help if maybe I added another resistor to the circuit, and If I did, would I install it in series or parallel. And about how many ohms?

I vote for a new light switch. Rheostats are like ballast resistors, when they're working they're working, when they're not they're broken. If the lights go out when you turn the switch knob the rheostat is KAPUT!
That's my story and I'm sticking to it!
(or....maybe recheck the wiring to the switch???)

Thanks for the reply Pasadena, but that's just it, the rheostat has current going through it but it just don't reduce the current as the contact slides across it.
I guess I could try another switch, but its really not that bigga deal. I'm just happy everything works. I rebuilt the harness about five years ago, just before I took the truck apart. Since then I've moved and somehow lost the wiring diagram I made for the truck. I had change some of the mires to different colors. What a freaking nightmare!
On top of that, right when I've got my multimeter hooked up to the coil wire to see if it gets juice when I turn the switch, the meter quit for some unknown reason, but I didn't know it at the time, and I spent about four hours bangin my head on the wall checking everything until I realized the only thing I hadn't checked was the meter itself. Sure enough. I stuck it to a battery and got nothing. That radio shack multimeter is in about a thousand peices on the floor.
Switched to my good old standby 1157 bulb with the wires soldered to it.
Everything works. All I gotta do now is put gas in it, prelube it, put the distributor in and fire it up.
Now if it would just get a little warmer.

I suspect the reason your dimmer is not working is because you have aftermarket gauges. The rheostat was designed to work with a certain dash that has a certain amount of lights connected to it. Whithout enough load, the rheostat will no get enough current to cause a drop across its winding. Try adding a parking light to the wiring and work your way up to brighter lights, like a brake light until you get the results you want.
Then mesure the resistance of that bulb and replace it with a resistor of the same value(or close to). Use a resistor that has a high wattage ratting so that it doesn't burn up.

Good luck

[ February 05, 2003: Message edited by: xtreme off-road ]</p>

To bad you destroyed you VOM it probably only needed a fuse. If you have an ohm meter isolate the dimmer switch circuit to the switch and check to see if the resistance changes when the knob is turned. If you choose to put a resistor in the circuit to cause the lights to be dimmer it would need to be in series with the circuit. The higher the resistance the dimmer the lights. It should not make any difference how many lights are in the circuit because they are all in parallel with each other. If it mattered then when one of them quit the others would get brighter.

Yes the lamps are all paralleled, but they are in series with the switch. The rheostat is an adjustable resistor, that controls the current to the dash lights. The load on the rheostat is important.
On newer vehicules it is a different case. They use a potentioneter (smaller version of a rheostat) that controls a voltage regulator for the dash lights. On this system, the number of lights does not matter.
It is like the difference between the old turn signal clickers and the electronic ones. The old ones would click slower if a light burnt. The electronic ones use a chip to regulate the flash rate, independent of how many lights are on it.

Yeah it probably was the fuse, but it was just an old cheapy that had a rough life, could hardly see through the plastic. I have a Simpson at work, but I hardly ever use it for anything but continuity checks.
Thanks for the ideas guys, I'll do both. First the ohms check on the switch. If that checks ok, then I'll start stacking bulbs in series. Cool.

[quote]Originally posted by Busted Knuckles:
<strong>If that checks ok, then I'll start stacking bulbs in series. Cool.</strong><hr></blockquote>
Add bulbs to the circuit, Parallel not series.