Dash lighting problem

[Calfdemon]

Ok, I normally do pretty well with wiring but cannot figure this one out.

Was working on CNM67's wiring the other day and now have a problem I can't wrap my head around. Prior to yesterday, his dash lights (blue wire with red stripe) were all working fine. No problems with that circut whatsoever. The dash was out, but the light above the cigarette lighter was still operational showing the circut was good when the lights were turned on.

I installed a stock 67 radio in his truck yesterday and never touched any of the wiring other than the red radio wire from the fuse box (his truck is a 67), and the speaker wires. Last night when we put his dash back together, none of the gauge lighting works. The problem is before the dash cluster plug because the light for the cigarette lighter (which is on the same blue/red circut) also is not working now, and that light works even when the dash is not plugged in.

So I have lost power to the instument lighting and for the life of me, cannnot trace the problem. None of the fuses in the fuse box appear burnt out, and just to be safe, I replaced the fuse for the instrument panel on the fuse box, and still no lights. The gauges all work though, just not the lights. Is there another fuse for that circut on a 67 that I am missing?

I know the lighting circut (blue/red wire) is controlled by the headlight switch, and can see where the wire goes in to the back of the switch. The rest of the headlight switch functions work as the headlights and parking lights all come on. So I would assume the switch is fine, but the blue/red circut is lacking power when turned on. Anyone have any ideas with this one? Again, this is on a 67 so some of the wiring is slightly different, but I have been going through and cannot find the source of the problem, and these lights were working on Wednesday.

Unfortunately, the 67 wiring diagrams available are not complete and the diagrams from the other years just dont seem to help due to the differences in the wiring.

Thanks in advance for any help.

[Bummer72]

I've been down this road....
Check out the headlight switch. On my 72, there was a ton of corrosion in it, and the rherostat (the springy looking thing wrapping around a ceramic wheel) doesn't make good contact. It is controlled by twisting the headlight switch knob, making the dash lights dimmer or brighter.
To remove the switch, first pull the wire harness connector off the back of the switch. Then, theres' a button under or on top of the switch assbly that will allow you to pull out the shaft of the knob when it's depressed. Then just remove the bezel nut from the front of the dash and pull out the switch.
Hit it with a little emory cloth or contact cleaner, re-install, and you will hopefully be good to go.
YMMV, but that's what I did.

[Calfdemon]

Good call, I will give it a look next time I have the truck in front of me. I didn't think to pull the switch and check it because we just recently replaced it. The switch in there now is the one from my 72 which was in good working condition. We trashed the original 67 switch as it was completely messed up and falling apart. But a gremlin got in the system somewhere between Wednesday and Thursday, so the switch might actually be the location. Thanks again, and I will check that out. Hopefully thats it. Anyone else have any ideas I might be overlooking?

[basketcase0302]

2nd the switch Rich. Check to see if you have power on your blue w/ red stripe. The rheostat is a common failure issue. You can sometimes pull it out and clean the contact with sandpaper to get a little more use from it.

[Calfdemon]

Thanks for the input guys... Just wanted to post an update on this problem and what the solution was. I am still baffled as to what exactly happened and how it happened, but it is fixed now.

The headlight switch was fine. Took it out, examined it, cleaned it, and put it back in. Still no dash lights... I got out my tester and there was power leaving the switch on that circut and the bulb would dim with adjustment of the headlight switch, so no problems there.

I tested the pin for the dash cluster which is also the spot where a continuation wire goes back into the wiring harness to light the cigarette lighter lamp (2 wires from the harness to the pin connector). There was no power at this pin or the wire going to the pin. Now, where the wire leaves the headlight switch and goes into the harness, to the point where it leaves the harness and goes to the pin, is an approximately 1 foot section of wire. Somewhere in this 1 foot section, wrapped inside 44 year old electrical tape with all the other wires, the wire lost connection and was not delivering power. I cant figure out how that could have happened as I did NOTHING to the wiring harness or that section of wire.

Anyway, I ran a jumper wire from the section of the wire just outside the headlight switch, to the section of wire just outside the pin for the dash harness. Once that connection was made, all of the dash lights and cigarette lamp now work. So again, a wire that never moved, in the middle of a harness that has been taped up for 44 years along with all the other wires, just decided to stop making connection. I dont get it, I dont understand it, I have never seen that before, but once I put the jumper wire in there, everything works now. So thanks for the suggestions, but although I got it working, I still cant figure out why it stopped in the first place..

[Bummer72]

Fusible link inside that cluster of wires under the tape?
That would be my guess. But only a guess,

[Calfdemon]

If the wiring harness had been hacked in any way or any modification to the original harness was made, I might think the same thing. But this is the original 67 wiring harness and it is untouched and unhacked. They did not run fuses in that section of the wiring from the factory, so unfortunately, that is not going to be the reason. I wish it was so I could wrap my head around what happened, but it still baffles me.