72 Chevy truck dash tach question
 

Original tach dash, Does anyone know what this hole is above wire terminals?

Re: 72 Chevy truck dash tach question
 

There was tape over it, but it is an access to the calibration screw.

https://www.67-72chevytrucks.com/vbo...1&d=1399779747

https://67-72chevytrucks.com/vboard/...1&d=1479521359

Re: 72 Chevy truck dash tach question
 

Anyway to test tach before I install?

Re: 72 Chevy truck dash tach question
 

Know any with a distributor machine? It would be the best way to check the calibration over the RPM range.

It's also pretty easy to hook the tach up with some temporary leads under the hood. You can verify the calibration with a new style digital timing light or a dwell meter.

Re: 72 Chevy truck dash tach question
 

thanks for the help

Re: 72 Chevy truck dash tach question
 

Just connect the wires to the tach output on an HEI or coil on regular distributor and positive terminal on the battery. I think you also have to connect a ground wire to one of the small screws on the back of the cluster to provide a ground for the the tach.

I can't remember off the top of my head which wire goes where.

Re: 72 Chevy truck dash tach question
 

It should be like this if you have an original factory tach.