I am not sure how to test one without a tachometer. There is not much to them. The only internal components connect between the IGN and TACH terminals. Below are a couple pictures of what the internals look like. I tried ohm testing across the IGN and TACH terminals and it does not seem to register. I know this one is working because it is the one I use for testing.
I will say that around 75 percent of the pedestal tachs I test are dead but I have never had a dead monitor. I believe the tachs get fried quickly if they are used without a monitor.
Jason
