I have several 1st gen tachometers that have been laying around for years. There is no way I can remember which cars they came out of, must less if they worked or not. Is there any way to bench test these things to see if they work? I thought about rigging up an engine compartment testing harness and trying them on one of my running camaros. Any advice would be greatly appreciated. :)

It's nearly impossible. For one thing, it takes a variable frequency source and that source will have fairly hostile voltages present. Not easy at all to simulate even with a frequency generator. About the only thing I can think of is to use a distributor machine and connect the tach to a distributor while it's spun up to various RPMs. Perhaps even easier than that would be to wire them up to a car. Beware however that many of the old OEM tachs were meant to work with breaker point ignition. Using an electronic ignition as a tach signal is hit or miss - it may work and it may not.

hook a hot wire to the dizzy from a battery spin it with a drill and see what happens, in theory this would work...oh and put a sprk plug in the circuit to give a plcae for spark to go...ground it on the same thig the dizzy is ground on....?
HEI would wok better but a coil may be easier for u?

Hook one wire to the negative side of the coil...tach lead...brown wire.
Hook one wire to the +...ignition hot...usually a pink wire.
Hook another to -...ground...black wire.
Fire it up!
Instant tach tester.

Below is a link to pictures of bench checking the tach for my 1974 Nova:

http://rides.webshots.com/album/556174870srBxzA

While it's been a while since I did the testing I would think there is a relationship to the signals (frequency) being fed into the tach and what the tach should read to see how accurate it is or to be able to calibrate it if that could be done.

Jim