Tach dash questions.
 

I made a harness to hook up tach dashes to test. The test rig is a 71 with hei. I hooked up a 73 dash and the tach went to zero and stayed there. I also hooked up an 87 dash and it seemed like it was 2,ooo rpms high but it was working. I tried some mid-late 70s ones and all worked fine. Does that mean i have 2 bad tach heads? or is there something different about certain years using the same tach harness? Any insight? Thanks.

Re: Tach dash questions.
 

i was reading about this repair
http://67-72chevytrucks.com/vboard/s...=503733&page=2
maybe some are for 6 cyl?

Re: Tach dash questions.
 

A 6 cylinder tach should read 25% high on an 8. It may be a I6 tach or it may have a bad resistor in the DIP resistor pack.

Re: Tach dash questions.
 

Thanks for the info. I was wondering if the 73 dashes were better off a coil rather than hei.

Re: Tach dash questions.
 

They both run off the coil - lead. I've looked at the tach signal from HEI and Points with a scope. They were similar. Points make more noise but are the same otherwise.