Bench Test Tach off a Rallye Cluster

[CudaJon]

Hello!

I pulled my Rallye instrument panel (73 Cuda) to change out the voltage limiter and fix the Tach.  There is a sticker from 2007 from the "Tach-Man" in the back of the cluster so apparently the tach electronics were updated 10 years ago.  My question is I'm trying to parse the problem to whether its the cable/ignition or the Tach itself.  I do have a signal generator and I believe from previous blogs on this subject I can equate 120Hz to 1800RPM however what I don't know is the characteristics of the signal that would be coming from the ignition coil. e.g.  is it a square wave pulse and if so what is the amplitude, 12V? what is the duration of the pulse?   Yes I did call Tach-Man and he did not know.  Thanks!

[1 Wild R/T]

If you have a signal generator what the chances you have a lab scope?  Scope your ignition & duplicate the signal...

Or you can do what I do... Hook the tach up to the engine with a couple jumpers....  Ground the body & send the coil negative to the signal input...

[CudaJon]

I do have a scope but was a little concern starting the car with the instrument panel out and wirings hanging out. So at the very least the AMP wires need to be shorted together... Anything else I need to worry about if I start the car? - thanks

[1 Wild R/T]

Just bolt the ammeter leads together & tape them up....