Tach Not Working on Homemade test engine stand

We've got a homemade engine stand we've used for years to test and tune motors when we build one. Of all the guages we have mounted to it, we've never had a tach so pulled out one today that we knew 'used to work' long ago. We mounted green wire to HEI tach terminal, black to ground, and tried red in a lot of places like battery, resistor, and battery kill switch. What we get is a needle that can bounce sometimes but will never show what rpms we're running, even when we hit the throttle. I know you don't need a resistor to run HEI but sometimes we use a points distributor and like the resistor mounted where it is. Resistor is hooked up currently and motor runs fine. Just need some thoughts on why the tach's not working...Our test motor stand does not have a fuse box. thanks,

"Sounds" like it's wired right (although there is usually another wire for the tach light, there is a possibility that the green wire you are using could be for the light instead of tach signal). Make sure your connection are good, and from there..... 'used to work'.....might be the operative term.


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Yeah it has the white/light wire but we don't need. You're right it could just be the tach's just done.

Can you temporary wire in the tach to another vehicle/engine? Just as a test?

Update: Thanks for all that posted. Bought a new tach, wired it the same way I had the old one and 'walla' its working like a charm. :)