GRAND PRIX Tach Help

85GrandPrix#1

Not-quite-so-new-guy
Jul 17, 2022
5
1
Colorado
Hello all, I recently posted about some tach troubles. Well I have it all in the dash, mock jumper bar and everything. Signs of life, but no life. When ign is on, it jumps to zero, so I know it’s getting power. When I start the car, no rpm’s show up. I can tap the needle and it’ll go back to zero, but no rpm’s. Tried the jumper bar in both the 6 cylinder and 8 cylinder configurations and both had the same results. Anyone know what’s up? (Pic with volt guage to show engine is running)
 

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79 GP 4 speed

Master Mechanic
Nov 12, 2017
420
63
Did you hook a wire up to the distributor?
 
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79 GP 4 speed

Master Mechanic
Nov 12, 2017
420
63
I have 5 wires going to mine, one to battery, one to tach and 3 to the other plug. I have 3 plugs all together.
 

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buick7332

Master Mechanic
Oct 21, 2014
310
93
N.E. Philadelphia area
Hello all, I recently posted about some tach troubles. Well I have it all in the dash, mock jumper bar and everything. Signs of life, but no life. When ign is on, it jumps to zero, so I know it’s getting power. When I start the car, no rpm’s show up. I can tap the needle and it’ll go back to zero, but no rpm’s. Tried the jumper bar in both the 6 cylinder and 8 cylinder configurations and both had the same results. Anyone know what’s up? (Pic with volt guage to show engine is running)
The white needle tach is from an older Grand Prix. I don't know for sure but I can remember reading a thread on this site about the difference between white needle and orange needle gauges. I think 84 and up are orange and would need some modifications. Maybe someone else knows more about this and can chime in.
 

DSM

Apprentice
Feb 1, 2008
57
8
Michigan
If the car originally had a clock then the circuit from the distributor "tach" terminal to pin 7 of the cluster plug (upper left, white wire) isn't going to be complete. Try temporarily running a jumper wire from the distributor to the tach pin on the gauge.
 
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Longroof79

Rocket Powered Basset Hound
Oct 14, 2008
11,667
113
Gainesville, Fl
If the car originally had a clock then the circuit from the distributor "tach" terminal to pin 7 of the cluster plug (upper left, white wire) isn't going to be complete. Try temporarily running a jumper wire from the distributor to the tach pin on the gauge.
Bingo! I was going to suggest checking to see if the white wire from the harness was connecting to the distributor.
 

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