Let me start with this:
I HATE ELECTRICAL WORK. I really didn’t pay attention in Shop class (yes I’m that old) nor in 4H when we made lamps. Plus I had a few mishaps during several attempts to repair things. Once I was drilling a hole with an electric drill in a an aluminum door and hit a wire hidden by the previous home in the frame. The drill bit exploded and I fell off the ladder and my drill fried. Add that to a few fried wires, radios and computer boards during failed attempts at soldering and you’ll get a well rounded picture of my electrical wheelhouse. Oh, toss in the fact that I’m colored blind and well…you get it.
I’ve a bit better experience with cars, but not enough to be comfortable.
Thanks for checking.
Tim
Over on the Average Guys Restoration blog there is a knowledgeable engineer that explains how the modern tach works and even how to bench test it. I think that very knowledgeable gentleman was using a 1968 Road Runner tach as his example. You should check it out.