Dimmer switch causes gauges to peg max!?

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nates68

nates68

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Puyallup, WA
Working on sons 67 dart.
Whenever I turn parking or headlights on, if the dimmer is on at all (dim or max it doesn't matter) the gas and temp. Gauge goes to max quickly. Also the left hand blinker dash light lights up. I replaced the headlight switch with a new one, same problem.
Somehow there is a short that feeds power from dash lights to the gauges.
Any insight?
Thanks!
Nates68
 
Check under the dash for any melted wires. The wires could have overheated and melted some insulation off...
 
I would look at the back of the inst' panel, printed circuit board, contact pins, wiring. The boards with pin in straight rows close to the top are weak/easily damaged.
 
Yeah,I think this model has a 5v dash gauge regulator.And it appears that your gauges are receiving full battery voltage, instead of the pulsed and averaged 5v signal from the regulator. I would disconnect the regulator and if the problem persists, then I would remove the cluster from the car and hunt for the cross feed.

It could also be that the dome lite wiring in the 8-pin connector behind the left kickpanel, is feeding power into the fuel gauge (which is connected to the temp gauge, thru it) sensor wire; they are side by side in that connector. There are other wires in that connector also that could be shorting. I would go here first,lol
 
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When I saw "dimmer switch" in header my mind went to the high beam low beam switch. But away... I just remembered a case from a few years back where a member had similar faults. The dash wiring harness was held up above the instrument panel with metal strap(s). A strap had chaffed through wires. A fuse blowing short wasn't present but 2 wires were burned/shorted together. Good luck with it.
 
All good info guys! Will do the dash boogie again. To be clear, all the gauges work just fine as long as there is no power to the panel lights.
Nates68
 
Make sure your cluster has a dedicated ground to the dash frame while you are at it, as it sounds like it could be a loss of ground feedback.
This is always a consideration when lights that are not supposed to light, do.
 
Do you have the original connector for the light switch? Or is it melted like mine was.
I built a wire harness to eliminate the burnt connector. On the switch the wire going to I feeds the Instrument fuse (as small as 3 amp maybe) It leaves there as E2 and connects with wires E2A and E2D E2E. E2D goes o the instrument panel and (Wire E2D) feeds the Radio. E2E feeds the automatic transmission indicator light.

I tried to upload the schematic, but it is too large. If you PM me your email, I will send them to you

2013-07-18 13.22.02.jpg
 
Ugh, my back is sore...
OK spent some time today:
-Headlight switch connector looks good, no burned areas, etc.
-found a small rats nest of wires from previous owner that was spliced into the 2 prong connector at base of steering column, not sure what that was about, got rid of it
-pulled fuse box down and inspected everything for melting, etc.. it looks fine.
-pulled flat connector that feeds power to temp/gas/lights off back of panel, pulled connector that powers lights out,and reconnected it to dash. Figured it could be driven with those lights out until we fixed the problem but...
When the LH blinker was turned on it flashed weak, intermittent and the gas/temp gauges started climbing fast, hmmm...
Reached up behind dash and wiggled the bulb that lights up blinker, the voltage limiter, few others.
Now it works fine, even after I put the light connector back in to the flat connector.
Feel like it's a fluke, maybe bumped some shorted wires, but so far can't make it go bad. Still need to add ground straps for reliability, but I was getting tired and cold
All good advice, will report back on how it's doing.
Nates68
 
Depending on the condition of the gauges, a full 12+ volts can fry them in 3 to 5 minutes. What will you do when this fault reappears out on the road? Will you be more focused on the gauges than the road ahead?
2 prong connector at base of steering column sounds like the reverse lamp switch. Those can be modified for several reasons. Column shift to floor shift conversion, later model automatic or a manual trans with reverse lamp switch at trans. And in some cases, the little plastic post coming from inside the column that activates that switch is broken. Owner puts a manually operated ( toggle ) switch in the car so to pass safety inspection. Good luck with it.
 
RedFish,
I agree with you on finding the source of the problem. It seems to be either the wires behind the cluster, or the cluster itself. We have been busy with a full suspension/steering rebuild and we're working on this electrical issue as well. Will be pulling cluster out again to look it over and make some ground straps.
Thanks
Nates68
 
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