Tachometer stopped working

[Charger Fan]

Had taken the plastic Rally dash bezel out to repaint and redo the wood grain. Taking me longer than expected thus I started the car up only to see the tach move up very slowly and then stopped. Prior to removing bezel the Tach had worked with no issues. The tach didn’t react to the throttle pumps while engine was running. Then after shutting engine down lt stayed where it where it had climb to (see photo). I made sure there were no metal to metal contact between back of instrument cluster and frame work behind dash before starting the engine. The two connectors that go to the tach (blue and gray wires) are still attached. What would cause the tach to do what it’s doing. All other gauges worked fine.

 

[bcOH67]

Did the lense get pushed tight again the needle somehow? Happened on my car, the needle got wedged around 2k.

 

[Charger Fan]

Nope, not the lens.

 

[Cranky]

Had taken the plastic Rally dash bezel out to repaint and redo the wood grain. Taking me longer than expected thus I started the car up only to see the tach move up very slowly and then stopped. Prior to removing bezel the Tach had worked with no issues. The tach didn’t react to the throttle pumps while engine was running. Then after shutting engine down lt stayed where it where it had climb to (see photo). I made sure there were no metal to metal contact between back of instrument cluster and frame work behind dash before starting the engine. The two connectors that go to the tach (blue and gray wires) are still attached. What would cause the tach to do what it’s doing. All other gauges worked fine.

View attachment 1842970

Years ago I pulled the dash cluster out a bit to change the bulbs. Once all the bulbs were replaced, I pushed the cluster back in but didn't screw it back in. Turned on the lights and went to turn on the key and everything went nuts. After scratching my head a bit, I screwed it in and everything was fine. It needed to be grounded. May not be your problem but it could be?

 

[Billccm]

Not familiar with that particular cluster, but phenolic circuit boards are very delicate once they age. Contact pins that are just pressed or riveted to the board get loose or build up thin layers of oxidation. Also, traces can be stretched as the PCB warps over time and creates very fine cracks.

You could have disturbed the board enough to cause any of these issues, or it's something simple like a connector not seated well.

Visual inspection with the cluster out is a good first troubleshooting step if all connections are seated.

 

[Bee1971]

How did you get the bezel off without removing the gauge cluster as a whole

That must have been fun , with all those screws laying on your back Yikes

I would have dropped the steering column and removed the gauge cluster as a whole


Is it a factory installed tachometer ? What year B Body 71- 74 Looks original or did you add it yourself

If so follow your signal gray wire , depending upon year on how it either goes thru bulkhead connectors to the negative side of Ignition Coil