Again, this is for the guys who aren't going to do that, atleast not right off the bat, especially if it's a working amp. As long as the "other components on the same circuit" are within operating specs(the tach amp operates) then using this many resistance readings can establish a general baseline to rule in/rule out an amp.

This compares 15 different resistance measurements to 15 measurements of any other amp. For example this working amp had one 0L/Infinity reading. My non-working amp had eight 0L/Infinity readings. I think such a comparison can actually be quite useful. If I was coming here blind with doubts about my tach amp and all I had was a DMM and those were the readings I got I would easily call it dead, which it is. THAT in turn takes me to the decision to replace it, repair it myself, or send it to someone who repairs them. Anyone who makes it this far has either seen the tach amp repair threads already or they'll find them soon enough. It usually comes down to time vs money. Is the juice worth the squeeze?

I already dissected my dead one when the replacement was en route and it had a few burns on the upper disc. Maybe I'll go through it some day but for now it's the cruise amp. That one will be re-soldered and re-resistored.