Hi smart guys.

The '65 cuda is doing well as a daily driver now. reliability has come along fine.

But, I've got a sticky rheostat on the panel lights and as I was driving the other night and messing with it the gas gauge & the water temp gauge stopped working and dropped to zero. The next morning they worked fine (possibly since the headlights were off) and seem to be working ok again even with the headlights on.

My 1st thought is to replace the sticky rheostat.

I welcome more reasoned thoughts on why a sticky rheostat would kill power to the gauges.

ddonner

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1965 Barracuda

Coincidence, methinks.

Headlight draw could affect power supply to the instrument voltage regulator, but it's not likely to kill it totally like that.
I think your IVR needs replaced (do the solid state upgrade!), and while you're in there, clean the contacts on the light switch (they are exposed once the switch is out of the dash) or just replace the switch.

The only other possibility I can think of is that the instrument panel is not well grounded.
I think the dash lights use the same ground path as the IVR, so switching them on overloads the connection.
I will check tomorrow, but I recall that the IP grounds through its mountings (4 screws that attach it to the dash).

That doesn't mean the old points IVR isn't still crap, though...

Based on personal experience with my 65 Valiant.

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O==\=/==O

"A mechanic is Somebody."
- Jim Preston

Probably too late, but was your charging system working, or did you lose that too? I'd be thinking bad connection, bad/burnt spade connector in a plug somewhere. My $0.02.

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"Louise", a 1976 Dart Custom project, (now sadly reverted to being just an "organ donor" to our other project Darts.)

Dash (orange wire) & dome light (yellow wire) circuits are not connected or part of fuel and temperature gage feed. Therefor messing with dimmer dashpot had nothing to do with gage failure. That said, a poorly grounded gage cluster would cause dash lights to fail as lighting circuit use screws securing gage cluster to dashboard steal frame as ground path. Both gage circuits work the same using sending unit at tank & head as ground path, and sharing common 5v feed from limiter. If the dash gage cluster were to lose its ground path it would effect the limiters operation causing an open circuit, and killing its 5v flow of electrons to fuel & temperature gages.

As above, rheostat can be cleaned with cleaners found at say Radio Shack, but for a few more bucks over cleaner cost one can probably purchase a new headlight switch.

It would be a good idea to pull the gage cluster and clean all its connections, and make a ground path via a length of #10 gage wire between cluster and body of car in addition to its mounting screw path. Redundant ground paths are helpful particularly at head lights, and charging system devices as well.

This leaves the 5 volt voltage limiter, and whether to trust it, or replace with solid state device home made or purchased. The thing to keep in mind is this: if the old mechanical points limiter fails with its points closed** both the temperature and fuel gage will get fried with a full 12 v; if it fails open, that is points not touching, the gages just don't get any voltage and stop working unharmed. As Dirty Harry would ask; "do you feel lucky"?

** A stuck points closed sign would be seeing both gages pegging to full and hot. Sometimes one will see these gages drift to right hold there for a few seconds, and then return to normal. This can be a warning sign limiter is acting up.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Most likely the instrument panel is not well grounded. When the lights are off there is a path to ground for the instruments, but that ground goes away when the lights are on. Yousee this frequently on tail lights that go out when the brake lights come on.

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Joshua

BTW, if I recall correctly off the top of my head, the dimmer rheostat to the instrument lights feeds power off of the headlight circuit, and not the same circuit as the other instruments.

Power, yes, but all the instrument bulbs ground though the IP frame to the dash, same as the IVR.

_________________
O==\=/==O

"A mechanic is Somebody."
- Jim Preston

^^^ Right, there is no common power feed to the 2. The ground would explain why he lost lights and water/fuel guages at the same time.