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Intermittent Panel Lights
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Kato
Posted 2023-01-20 10:42 AM (#627107)
Subject: Intermittent Panel Lights


Member

Posts: 16

Hi, everyone. I have reviewed many threads about panel lights, but I haven't seen this exact problem and was wondering if anyone had any insight. My '56 DeSoto is original and, so far, seems unmolested, including the wiring harness. The panel lights come on with the parking or headlights, as would be expected, but they will sometimes cut out abruptly after being on for a bit. I haven't noticed a pattern for this yet -- I once drove almost half an hour with the headlights on and had no issues, last night they cut out within a couple of minutes. They then came back on several times, and went back out again, sometimes immediately, sometimes after 10 seconds or more. This pattern does not seem to correlate to hitting bumps in the road. When they go, I hear a light metal clunk/click, and sometimes see the ammeter dip all the way to discharge (as if it's also lost power) but the ammeter comes back immediately even if the panel lights don't. Although the headlights flicker a touch when the panel lights go, they are fully on while the panel lights are off. The sound and fact that the panel lights try to come back on makes me think this is a circuit breaker that's beginning to fail, but looking at the wiring diagram it looks (to me) like a headlight circuit breaker that cuts out should killl the headlights when it goes, and that isn't the case here. While the lights are out, turning the dimmer switch for them does not cause them to come back on.

If I should remove the light switch to clean the rheostat (even though turning it doesn't fix the problem), does anyone have a procedure for doing so? The shop manual does not go into much detail on removal of the switch.

Thanks!
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Viper Guy
Posted 2023-01-20 11:03 AM (#627108 - in reply to #627107)
Subject: Re: Intermittent Panel Lights



Expert

Posts: 2003
2000
Location: Branson, MO
It's not a bad idea to remove the switch and clean it. If that doesn't do the job it'll probably need a replacement. There may be others on the forum that can add to the discussion.
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Kato
Posted 2023-01-20 11:40 AM (#627110 - in reply to #627108)
Subject: Re: Intermittent Panel Lights


Member

Posts: 16

Thanks for the response. After looking for a replacement switch online, I just went out and poked my head under the dash: the wiring is all original and is in shockingly good shape. I noticed that there's a wire running from the rheostat to the headlight switch, and checked for loose connection at either end. I managed to pull the connector out of the back of the switch and, although I didn't see any corrosion, I wire brushed the connector and plugged it back in, which created a small puff of dust. It's very possible that a little corrosion in that connection was my culprit, and that the click I was hearing was just the circuit being opened by excessive local heat, then closing when it cooled off. Won't be able to verify until it's dark out again!
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ronbo97
Posted 2023-01-20 2:52 PM (#627119 - in reply to #627107)
Subject: RE: Intermittent Panel Lights


Expert

Posts: 4036
2000200025
Location: Connecticut

The dip on the ammeter is concerning. It sounds like a loose wire. There may be a momentary short as well. 

Just because wiring 'looks good' doesn't mean that it is. Your car has the old cloth wiring, which after almost 70 years is probably not in good shape and is more flammable than the later vinyl wire. I'll bet the wiring in the engine compartment is much worse, and is covered by several layers of electrical tape. I'm a big fan of rewiring any pre-1957 Mopar, since I'm not a fan of car fires.

Ron

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Powerflite
Posted 2023-01-20 5:00 PM (#627127 - in reply to #627107)
Subject: Re: Intermittent Panel Lights



Expert 5K+

Posts: 9663
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Location: So. Cal
I agree Ron. The ammeter dip is very concerning. Sounds like a temporary short somewhere so you need to find where that is.
Usually flickering dash lights that aren't caused by something else shorting out, come from the rheostat that dims the dash lights. Take that out and clean the contacts up really well.
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Kato
Posted 2023-01-20 6:22 PM (#627138 - in reply to #627127)
Subject: Re: Intermittent Panel Lights


Member

Posts: 16

Powerflite - 2023-01-20 5:00 PM

I agree Ron. The ammeter dip is very concerning. Sounds like a temporary short somewhere so you need to find where that is.
Usually flickering dash lights that aren't caused by something else shorting out, come from the rheostat that dims the dash lights. Take that out and clean the contacts up really well.


Yeah, the ammeter is what's making me a bit nervous on this one, although it coming right back up while the lights stay off (but headlights stay on at same brightness) makes me question the idea of a short. I'm also looking sideways at the rheostat, although in my experience they usually lose the circuit in specific locations along the coil, and turning the knob would then find a better spot and I'd get lights back that way (been down that road a couple of times, ended up just wiring past the dimmer in my '51 Hudson) -- it also doesn't jibe with my experience that the lights would come back on with the knob in the same location if the rheostat coil was the issue, although I'm not discounting it, it's just not my prime suspect right now. I'm hoping that cleaning up the blade connector from the rheostat to the switch turns out to be the answer and that the ammeter is dipping due to some feedback from the circuit cutting in and out, but I'll keep testing and investigating.

By the way, you've responded helpfully to several of my posts now, wanted to say thanks for doing so and (because no good deed goes unpunished) ask you a question: I see the allen head under the headlight knob, if i remove the knob, does the ring that controls the dimmer slide forward and off, revealing a nut that holds the switch in place?
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chstrumpetdude
Posted 2023-01-25 9:24 PM (#627242 - in reply to #627107)
Subject: Re: Intermittent Panel Lights


Regular

Posts: 57
2525
Location: Springfield, MO
I am unsure about 1956, but 1959 has it at the front of the switch and is a white ceramic housing with the coil facing the knob. Mine also had intermittent lights and I cleaned the coil and coil contact to fix the issue. I would move the knob to a new location and see if it still does it, but you probably will need to remove it (not fun with the seat in) and spray some electronic cleaner in there. I picked up a masterforce 1/4 flex driver that is a stiff metal spring as a shaft to aid in removing car gauges. You can torque it pretty hard.

Unfortunately 1959 switches were not really meant to be disassembled. The guts come out via the rear and the whole thing held with the housing crimped inward at 4 locations. I ended up crimping them back, but not 100% as before and partially glued it back there. I don't recommend it and if you can spray it out with cleaner first is easier.

I figured that if it lasted 60 years with who knows how long being derelict outdoors, it should last way longer than my lifetime being kept in a garage.
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