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Strange electrical gremlin...'71 Demon 340 rallye dash #1403139
03/16/13 11:57 AM
03/16/13 11:57 AM
Joined: Jan 2003
Posts: 1,180
Willoughby Hills, Ohio
gd9704 Offline OP
super gas
gd9704  Offline OP
super gas

Joined: Jan 2003
Posts: 1,180
Willoughby Hills, Ohio
Hey gang, long time.....

Two years ago I rebuilt the voltage regulator in my rallye dash with solid state guts. My dead fuel gauge came back to life, and I was happy.......

Last summer, I noticed when I had my lights on, the fuel gauge would peg past full. A bit of fiddling and I found out it was directly related to the dash lights-dim the lights, the fuel gauge went back to normal. Turn 'em up, fuel gauge peg.

With spring looming, I'm working up the courage to pull the dash and poke around looking for what's causing this.

I welcome any hints, tips or past experiences that might guide me in figuring this out.

The older I get, the less I enjoy being upside-down under a dash having 40 year old insulation, dust and God-knows-what-else falling in my eyes.....

Re: Strange electrical gremlin...'71 Demon 340 rallye dash [Re: gd9704] #1403140
03/16/13 12:25 PM
03/16/13 12:25 PM
Joined: Jul 2003
Posts: 6,167
Maryland
GO_Fish Offline
master
GO_Fish  Offline
master

Joined: Jul 2003
Posts: 6,167
Maryland
my standard answer on this is check your grounds. Electrons start looking everywhere for a path to ground when a good one can't be found. All kind of strange things happen. Install toothed star washers on your ground connections, maybe install a designated dash to body ground strap?


Scott B. "I'm a self-made man... I started with nothing, and I still have most of it!" 68 360 rusty B'cuda 'vert (GO Fish)13.59@ 98.72 mph 69 340 GTS stock 14.18@ 95.60 mph 01 5.9L Ram 1500 Quad Cab 4x4 01 3.5L 300M 16.23@ 86.97 mph
Re: Strange electrical gremlin...'71 Demon 340 rallye dash [Re: gd9704] #1403141
03/16/13 12:27 PM
03/16/13 12:27 PM
Joined: Nov 2003
Posts: 35,957
Lincoln Nebraska
R
RapidRobert Offline
Circle Track
RapidRobert  Offline
Circle Track
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Joined: Nov 2003
Posts: 35,957
Lincoln Nebraska
not sure how it's doing it but as you said probably have to pull the dash & see where/how the orange wire dash light circuit is bleeding over to the fuel gauge circuit & in the meantime I'd disable the dash light orange wire circuit to avoid any damage tho you'd think if it was permantntly damaging it it'd have done it by now but never hurts to be cautious. I'd drop the column a bit then drape a rag over the column to protect it then pull the dash (remove a batt cable first)


live every 24 hour block of time like it's your last day on earth
Re: Strange electrical gremlin...'71 Demon 340 rallye dash [Re: gd9704] #1403142
03/16/13 12:57 PM
03/16/13 12:57 PM
Joined: Feb 2003
Posts: 8,472
A
Andrewh Offline
master
Andrewh  Offline
master
A

Joined: Feb 2003
Posts: 8,472
diagrams are here.
http://www.mymopar.com/index.php?pid=27

looks like red for the high beams and dk blue for fuel.

2 different parts of the board.

my best guess is 12 volts is bleeding over from that red line on the circuit board or your vr.

I don't see how, as they seem to be 2 seperate boards.

do you have the low fuel warning light?
as there is a place where the headlight delay and that relay tie in for power. but again, that should be before the vr.

as said above, the only other common thing is ground.

Re: Strange electrical gremlin...'71 Demon 340 rallye dash [Re: GO_Fish] #1403143
03/16/13 05:40 PM
03/16/13 05:40 PM
Joined: Jun 2008
Posts: 1,819
Colorado
D
denfireguy Offline
top fuel
denfireguy  Offline
top fuel
D

Joined: Jun 2008
Posts: 1,819
Colorado
Quote:

my standard answer on this is check your grounds. Electrons start looking everywhere for a path to ground when a good one can't be found. All kind of strange things happen. Install toothed star washers on your ground connections, maybe install a designated dash to body ground strap?


Most of the time when attacking a problem like this, your first tendency is to look for a short in the wiring. Most of the time, it is a missing, corroded or painted over ground point. Shorts are easy to find, high resistance grounds a pain in the lower posterior.
Good luck.
BTW, I would start with the new regulator and make sure it is grounded properly.
Craig


2014 Ram 1500 Laramie, 73 Cuda
Previous mopars: 62 Valiant, 65 Fury III, 68 Fury III, 72 Satellite, 74 Satellite, 89 Acclaim, 98 Caravan, 2003 Durango
Only previous Non-Mopar: Schwinn Tornado
Re: Strange electrical gremlin...'71 Demon 340 rallye dash [Re: denfireguy] #1403144
03/17/13 02:54 AM
03/17/13 02:54 AM
Joined: May 2006
Posts: 1,414
Stow ,Ohio
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demon440 Offline
pro stock
demon440  Offline
pro stock
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Joined: May 2006
Posts: 1,414
Stow ,Ohio
Post up some pics of your Demon.
I'm not much of an electrician but if you
need some help, I live near by and also
have a 71 Demon.

Re: Strange electrical gremlin...'71 Demon 340 rallye dash [Re: demon440] #1403145
03/17/13 03:01 AM
03/17/13 03:01 AM
Joined: Feb 2003
Posts: 4,613
Castlegar, BC, Canada
That AMC Guy Offline
master
That AMC Guy  Offline
master

Joined: Feb 2003
Posts: 4,613
Castlegar, BC, Canada
I would concur with everybody else on checking your ground. On my toys, since I like having all my gauges to work, I always add an additional, dedicated ground wire to the cluster. As has been said, bad grounds can cause all sorts of weird problems. I once saw a '69 Fury that had such dodgy tail light grounds, that when you turned the hazard flashers on, the tail lights would alternate like a cop cars' wig-wags!


Bloody Mary, Full of Vodka, Blessed art thou among cocktails....

Re: Strange electrical gremlin...'71 Demon 340 rallye dash [Re: demon440] #1403146
03/17/13 10:17 AM
03/17/13 10:17 AM
Joined: Jan 2003
Posts: 1,180
Willoughby Hills, Ohio
gd9704 Offline OP
super gas
gd9704  Offline OP
super gas

Joined: Jan 2003
Posts: 1,180
Willoughby Hills, Ohio
Quote:

Post up some pics of your Demon.
I'm not much of an electrician but if you
need some help, I live near by and also
have a 71 Demon.




I used to be a regular around here before my son was born....









It's a nice, numbers-matching driver that was restored in the 90's by a Moparts member.

I've had it for 16 years now.

Thanks, everyone for the electrical tips.

If I have to tear the dash apart, I may as well replace the dash pad......oh, does this sound fun.







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