Author Topic: Gauges lose reading  (Read 411 times)

JonG78TransAm

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Gauges lose reading
« on: June 14, 2018, 03:53:37 PM »
I have installed a new wiring harness, all gauges besides tach work fine. After warming up and driving for a bit I lose all readings. These are the original gauges that came with the car. Any idea why something like that would happen?

71455formula

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Re: Gauges lose reading
« Reply #1 on: June 15, 2018, 03:08:17 AM »
Bad ground somewhere. I would start with the common ground for the gauges.
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70RAIV455

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Re: Gauges lose reading
« Reply #2 on: June 15, 2018, 06:42:31 AM »
Bad Ground or Losing your +12 Vdc Power Source.

Jack

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Re: Gauges lose reading
« Reply #3 on: June 15, 2018, 10:28:07 AM »
More info is needs, the tach is grounded through the housing but gets power from the fuse box directly, are you also losing seat belt lights, directional's, brake lights, etc.?




Regards, Jack

firebirdparts

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Re: Gauges lose reading
« Reply #4 on: June 15, 2018, 03:12:15 PM »
There are multiple grounds involved in the gauges but only one power source.  If they lose power, they should just do nothing or drift by gravity, except for the volt gauge.  It would go to zero.  If they lose IP ground, I think the temperature gauge might go high.
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Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

Re: Gauges lose reading
« Reply #4 on: June 15, 2018, 03:12:15 PM »

JonG78TransAm

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Re: Gauges lose reading
« Reply #5 on: June 16, 2018, 11:33:56 AM »
All the grounds are connected and secure on clean steel.  I removed the gauges today and read OL on the back of the tach post. When I sent power to the tach through its power and ground the needle jumps. Through the back it doesn't, meaning through the circuit board I get nothing. I assume the circuit board is bad. A nut was loose on the back of the copper ribbon where the water temp gauge runs, hopefully that solves that issue. But what would be causing blown fuses. The thing has only driven 20 miles and random fuses are blowing. Ugh. 2 steps forward 4 back on this thing lately .

firebirdparts

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Re: Gauges lose reading
« Reply #6 on: June 16, 2018, 11:50:33 AM »
You can't treat fuses as random.  they're not.  fuses are specific.  Just take them one at a time.  You can measure amperage on a circuit that blew a fuse, monitor voltage on the whole system, look for "problem" wiring.  It's hard to say which of these things would be the easiest.  One thing you might do while it's apart is look for any kind of crossover things-touching-that-shouldn't on the printed circuit.  Any problem on the printed circuit will be visible. 

I'm a total fundamentalist when it comes to wiring, but that's not always the quickest path to the answer.  It's the sure path.
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

Re: Gauges lose reading
« Reply #6 on: June 16, 2018, 11:50:33 AM »
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