The Stovebolt Site Forums The Shop Area The Electrical Bay Instrument lights - LOL

On my way home from the local cruise night yesterday, my instrument lights started working….for the first time ever. Several guys had been looking inside the truck and I figured maybe one of them found something I didn’t know about. So I twisted on the light switch and they went out. Crap. A couple miles later they came back on and were still on when I got home.

Any of you have an explanation? I’d think a loose connection would make them flicker, but I didn’t see that at all. Isn’t there a rheostat in the switch for the dash lights? Is there something there I don’t understand that would produce such a symptom?

You nailed it! The rheostat gets corrosion on it and will act like that. Sometimes it can be cleaned but often the switch must be replaced. Try spraying contact cleaner on it and work the dash light dimmer sever times back and forth. You may have to drop the switch from the dash but leave the wires attached.

Does the dimmer operate by twisting the switch button?

Yes if you mean the pull switch knob. It operates like a radio volume control knob.

Gotcha.

The knob itself seems to turn freely but I can grab the square shaft and get maybe 90 degrees of twist

If you remove the headlight switch and place a bit of 600 grit wet/dry paper between the wiper and the coil and rotate back/forth you'll clean the coil...if the sandpaper follows with the wiper. Then if you reverse the paper and wiggle it a bit, you'll clean the wiper. Things will work much better.

Now if you have a replacement (think Chinese) switch, you have a coil with a different resistance value. The OEM unit had about 3.2 ohms of resistance, but it was actually created by engineers with degrees and a proper plan and not people just copying what they see. The Chinese switches have anything from 10 to 13 ohms resistance and it all has to do with what value of resistance wire they had to use the day they made the switch. I posted about this before when I explained how to resurrect your headlight switch and again just last week when I explained Kanthal wire values and the effect they had on light switches.

This isn't to say the Chinese switches won't work. They will, but when you turn the dimmer from fully bright to dim, you'll only have to turn the knob about 1/3 of a turn...because you run into an ohm rating too high to make your lights burn. Please remember resistance means just what it sounds like...the more you have, the fewer electrons make it to their target. That's also why these coils are set into ceramic pieces...so they won't get too hot. So instead of having a switch that gives you a nice full range of dimming, you get one which gives you a short range of dimming.

Thanks. This would be an older switch that’s been in the truck since at least the late 70s. I suspect it’s non-chinese

That could have been a Standard Products switch (very good...sold under many different brand names like Sears, NAPA, Western Auto, Wards, Gibson's, K-M and many others) or Echlin (which was once owned by Dana and later Standard Products) or it could have been one of some switches sold by Eaton and made by ???

All the ones made in the USA are good. Some were made in Mexico starting in the 80s...actually those were not too bad. When you get up to the 90s, a few were made in Taiwan (ok) and then you have the Chinese wonder switches.

As for Kanthal wire, many people around the world sell it. I've bought some from as far away as Croatia when I needed an odd size to get a specific resistance value. In case anyone needs it, here is a list of common round and flat types and their specs:
https://temcoindustrial.com/product...nce-and-non-resistance-wire/kanthal-wire

JW51 That chrome ring on the knob will get loose and rotate freely after the knob shrinks from years of drying. You can crazy glue it,kinda messy easy to take out to glue it !

Those GM rheostats used for dimming the instrument panel lights were awful. The one in my 1971 Camaro was lousy. The one in my 1980 3/4 ton was lousy. The one in my 2010 Sierra is good - it's a whole new design.

For the 54, I just moved the wire for the instrument panel lights to the same connector used for the running lights - so they are not dim-able. Works for me.

Gord&Fran Probably need to use it more to get corrosion off of the resistance wire coil.

The bakelite shrinks over time. You can dribble two or three drops of acetone on the back side of the stainless ring...let it run between the ring and the bakelite center, but don't use enough that it runs all over the place. The bakelite will swell a bit and then hold.