1969 Charger: Gauges go dead when I turn the headlights or parking lights on

[MaximRecoil]

I suspect this is the same situation as when the gauges get pegged to the right when turning on the headlights (like in this thread), but I have a solid-state gauge regulator in there (I've had it in there for about 10 years now) which has over-voltage protection, so instead of pegging the gauges it trips the protection circuit and makes the gauges go dead until the lights are turned off.

This just started happening without me having made any changes to anything even remotely recently. The instrument cluster frame has always been well-grounded, and I've had good grounds in general for the 12 years that I've had the car back on the road. Making sure that the main chassis to engine block to battery grounds were all perfect was a priority from day one; the car is better grounded than it was when it was brand new, since I used thicker wire (1/0 AWG for the main ground cable from the engine block to the negative battery post for example) and also added a short (about 6") 4 AWG ground wire from a factory stud on the firewall to a factory bolt on the rear of the engine block. I sanded all of the ground wire attachment points to bare steel before bolting down the ring terminals, and all the ring terminals are properly crimped to the wires. I've checked grounds with a meter many times over the years and it's always a perfect dead short from any part of the body to the negative battery post.

My headlight switch was acting up last year; sometimes when I turned them on, not all of the lights would come on. I turned the switch on and off a bunch of times in a row and eventually it seemed to come out of it, working on the first try every time, and it still does; haven't had it act up this year at all. I wonder if there's something weird going on with the headlight switch that could cause this particular problem with the gauges though.

[b5blue]

It's a long shot but with the cluster housing getting ground from the dash frame through mounting screws, loosen and tighten the cluster screws a few times. (Easy to do.) 

[MaximRecoil]

It's a long shot but with the cluster housing getting ground from the dash frame through mounting screws, loosen and tighten the cluster screws a few times. (Easy to do.) 

I've already tested continuity between the cluster housing and the negative battery post with a meter and it's a dead short.

After I made this thread I noticed some other weird things happening. For example, turning on the headlight switch to either the parking lights or the headlights sent power to some of the switched accessories, like the radio and the heater blower motor. I tried the windshield wipers too, but that cut power to those accessories, and didn't have any power for themselves.

In any case, I noticed that at least one of the dash lights wasn't working (the one for the gas gauge) so I reached back there and removed the socket+bulb and bench tested them; the bulb worked fine on the bench. I tried to put the socket+bulb back in but it was in a hard to reach area and I dropped it and couldn't find it immediately. So I tested things out with the socket+bulb not in there and everything worked exactly the way it was supposed to.

I'm not sure what fixed it; I can't see how the socket+bulb that I removed could have been causing those issues. What I suspect is those posts for the power connector; my hand bumped into that connector plenty of times while I was blindly trying to reach the socket+bulb to remove. I soldered all of those posts' flared mounting ends as a preventative measure over 10 years ago, because that's a very poorly designed connector; from the factory, nothing but those flared ends are making the electrical connection to the PCB. If one or more of my solder joints cracked there could be an intermittent connection there now.

I didn't take the dash out today to have a look at those connector posts / solder joints, because I ordered a new headlight switch so I'll have to take the dash out to install that anyway. When I do that I'll check those connector posts.

[b5blue]

  A few years back I rebuilt my cluster and installed an M&H harness set and within a month my speedo took a crap. 

[MaximRecoil]

A couple of the posts were loose, and when I removed my old solder from them, one of them simply fell off:



There was no good way to reattach it; merely soldering it back in place to a flimsy trace would be very weak without any mechanical support for it (the brittle flared end that provided some degree of mechanical support for the post from the factory broke off).

I decided to remove all of the factory posts since the others already had pieces of their flared ends broken off, and would cause more problems eventually.

I went to the hardware store and bought five 4-40 brass machine screws and matching nuts. The original posts are about 0.09" diameter, and 4-40 screws are a little over 0.1" diameter, but those were the smallest they had. I filed down the threads to make them the right diameter (I didn't touch the threads at the very bottom because I needed the nuts to be able to screw on down there). I also had to file down the nuts until they were round because the holes in the PCB are so close together that the nuts were touching each other.

After I installed the brass screws/nuts in the PCB holes and tested it to make sure the wiring harness connector would fit on there, I soldered short solid 20 AWG jumper wires from each nut to its respective trace, which also soldered the nuts to the screws, so they'll never loosen:



Finally, I filed down the heads of the screws so they didn't short against the cluster housing when the PCB was reinstalled, and also put a couple layers of electrical tape on the housing beneath the screw heads for good measure (I didn't actually need the tape; after filing the screw heads down they weren't contacting the housing, which I confirmed with a continuity meter).

It works perfectly and those brass screws/nuts make for a far more solid arrangement than the flimsy factory setup; I doubt I'll ever have any problems with that PCB again.

Also, the new reproduction headlight switch works perfectly; very nice quality too. It lined up with the mounting screw holes in the cluster housing perfectly, the vacuum switch doesn't leak, the chrome is perfect, and the clicks feel good.

[b5blue]

There ya go!