testing a tachometer

[irowiki]

HAs anyone here ever tested a tachometer?

I bought a (first gen) SR5 cluster for my 1st gen from a junker first gen and it doesn't work.

Did some digging and figured out there's 3 connections to the tach, 12v from the gauges fuse, ground, and "IGN -" (seems first and second gen tach works the same way).

I did some more digging and found out connecting my external tach to both the green plug on the igniter or the negative terminal of the coil(?) results in a reading.

If I connect 12 volt power to the +/- of the tach, what kind of power do I apply to the IGN - connection to test?

[Petros]

I think the IGN wire is the signal wire from the distributor. It uses the signal to "count" the rpm based on the number of spark signals. it is likely only 12v, but it would be a pulsing signal.