Inliners International Forums General Discussion Engines gm hei tach signal

I have an old handheld tachometer which I've used for years on breaker point systems; Can I use this on a GM HEI ignition by just reading negative side of coil??? I'm not sure, so thought asking may save me screwing something up.

ignition is late 70s GM HEI

thanks

Dear Johnny;

I've used my digital (Fox Valley) on the ones with the coil separate.

If It's an old unit with a meter, I would be safe & not do it. Why take a chance???

If the engine is running the dwell is okay on an HEI GM unit. It's ususlly a HV problem when they die.

Good luck, John M....