Xterrable

Well, I was having an issue with my dash lights in my 74. Where the fuse would blow at random time killing my dash and tail lights. So I got a new switch from Wilcox thinking it might be the problem as it was very worn and never locked into the one position. Always felt mushy and soft.

Well, I got the switch hooked up. Changed out 2 bulbs that were blown in the mean time. It was just about dusk tonight when I turned the lights on to make sure all the dash lights were working. After about 2 seconds, the dash lights went out.!! Crap.. So I turned the switch off. Wanted to make sure that it was the fuse, so I turned them back on and checked my tail lights to make sure they were out. But they were on!!!... Odd. Everytime my dash lights blew, i had no tail parking lamps. All of a sudden, I smell smoke... There is a ton of smoke coming from my dash. I quickly turned the switch off, unplugged the battery and started tearing into my dash to see where the smoke was coming from. Sure enough, it was my headlight switch... The harness looks fine, no burn marks at the wires them selves.

So I am stumped. Electrical issues and I dont get along. I can never seem to find out where they are coming from. Any thoughts on where the heck to start aside from tearing the steering column out and redoing the dash harness? I hate to get a new switch and have that melt to... Or have it melt 3 weeks from now when I am going down the road and the car catches on fire....


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...Roger...

I was hoping Ernie would jump in here but his wife might have pulled the plug on his computer tonight.

That almost looks like there's an extra piece of metal in that mess.
Did the INST fuse blow when this happened ?
It appears like the ground for the courtesy lights has burned in 2.

If the rheostat is burned in 2 and there is no foreign metal it would almost have to be from an overload of the Inst lights.
I would send this back to Ernie and let him dissect it and determine what circuit caused this.

I would use a jumper with an inline fuse to test before installing another HL switch.

Xterrable

Well, I just re-installed my original headlight switch. And it works.... As do the desk lights. So I did not durn the fuse out. No smoke. And I didn't do anything other than disconnect the batter to stop the old one from burning, and reinstall the old one....

On a side note. My old switch had a bad dimmer. The dash lights were always off, unless you had to turned to 100% brightness. Then they worked... Which is why I replaced it..

Looking at my burnt switch, it looks like I had the dash lights at Bout 70% brightness when It burnt up.. Could the rheostat have been bad? Of just. Bad spot And I just happened to be one it when it burnt....

I am really afraid that there is more to the story. That I am going to get it all back together and have it happen again when I am driving..

69 Chevy

Best to sell it now if it creeps you out.

Xterrable

69 - You making an offer??

I would not mind dumping 500 bucks into a new dash harness... if I KNEW it was going to completely solve the problem... For ever.

Electrical issues are not my forte.. And at this point, my wife is starting to rethink the new Corvette idea. It took a lot to get her on board. But now she is second guessing herself.

...Roger...

If you feel you still have a problem , I would jumper each circuit individually with a low amp fuse and monitor the situation.
By looking at the switch,I doubt that was fed by the 20amp TAIL fuse,which leaves the heavy HL circuit that is fused with the fusible link.
Ernie will be able to determine what circuit fed this.

Xterrable

On second thorugh, my wife reminded me that I did the headlight switch last week. Drove it last Monday afternoon and night. Worked fine. Then the Tach cable broke on the way home. That is why I was working behind the dash.... Got the new tach cable in, replaced a few bulbs and then put it back together. Thats when it melted... Once the dash was put back together.

... But as I stated, I tried the old switch with the dash pad "dislodged" and it worked fine..

Wondering if there is something getting piched when the dash in completely installed..... Could a hot wire touching the back of the dash cause this? Or would the fuse blow first?

...Roger...

That would depend on the fuse rating of the hot wire.
Looking at the switch,it looks like maybe the thin brass finger that grounds and turns on the courtesy lights has been forced into the rheostat. This might create a short through the rheostat,so it wouldn't be a direct quick short which would blow the fuse.
The finger could have been forced over by the small HL vacuum hoses going to the switch.

Xterrable

I think that is just an optical illusion from the photo. That thin brass finger is still about 1/4 inch from the spring. But has melted through the white insulator that it rides on.

...Roger...

OK , then what is the item with the arrow going to it ?

Xterrable

Melted/burnt plastic. When the switch is installed the arrowed area points downward. As the plastic melted it started to run onto the porcelain.

...Roger...

OK so that must be the plastic from the barrel the HL **** rod slides through.

Xterrable

Exactly!!

Something tells me that the problem did not start with the switch, but it ended up there...

I am hoping that it was just a bad switch, and the stars aligned and it caused the problem..

When you say jumer each circuit, are you suggesting put the everything back together but leave the switch unplugged. Then run a wire with an inline fuse from each plug on the switch harness to the switch? And see if any specific wire shows a problem?

The car is just so difficult as there is no room to look at the back of the dash once installed. Especially on a Vert.

7T1vette

The headlight circuit is pulling a lot more current than it should. Which means that there is some power wire in that circuit that has a partial short in it. It is most likely a wear-thru or a pinched wire that is rubbing some metal that is grounded. Unless there was some kind of dead-short built into that switch (possible, but not likely), the problem is in the wiring or the fuse block (again, possible but not likely).

Your best approach to find the area of the fault is to disconnect the battery and use an ohmmeter to look for continuity between the power input/feed wiring in the headlight circuit and ground. Remember that the headlights have resistance in that circuit; it would be best to disconnect them so they won't influence the results. Also, the dimmer in that switch feeds the dash lights. That power feed source could also cause that problem; but, one would think that the INST fuse would have blown, if that was the case.

Xterrable

Yes, that is my fear. I think that when I put the drivers dash pad back into place, something got pinched. I guess at this point, I need to pull the steering column and actually take the drivers dash out. Thats the only way I can ever imagine getting eye's on the wires.. And if I go that far, a new dash harness might be in my future.

0Willcox Corvette

In looking at this my first thought is there is power on a ground wire. Pinched, touching, arch'd... I don't know. Do any of the terminal on the switch show a sign of being hot?

The white wire is the courtesy lamp ground. If power is on this wire the rheostat and the porcelain will get scolding hot.

0Willcox Corvette

If you want.. mail the switch to me and I'll tear it apart and take a look inside for a problem. This would at least narrow it down.

But.... I think if you pull the dash pad out you're going to find the issue. If you don't see it at first, peal back harness tape and keep looking for a melted wire. With that much power hitting the switch I'd think you'd see something pretty quick.

Xterrable

None of the terminals on the swtich appear to have gotten hot. BUT, the courtesy "finger" after passing through the porcelain does have a burn mark in it. After going throught the porcelain, it turns and passes under the plastic barrel. Before turning but after the copper rivet there is a black line across the "finger"..

I can take a better picture tonight when I get home. Cant get to the pic hosting site from work...

Xterrable

Thanks for the offer. I would live to have you look at it. Do you want addressed to anyone?

If it is the courtesy lights, what is on that circuit? Just the 2 lights under the dash and the door switches?

lionelhutz

Blowing the fuse for the dash lights randomly and then you burned-up the dimmer on the new switch. Somthing is randomly shorting the dash light circuit. You old light switch set at 100% brightness for the dash lights would blow the fuse. The new light switch set at partial brightness burned up the dimmer rheostat instead since the rheostat limited the current enough the fuse didn't blow.

You need to take a good look at the dash harness and the circuit boards. Likely a bare spot on the harness wiring that grounds out when you hit a bump then breaks loose a few bumps later after causing the damage.