Magneto/tach ???

Questions are to do with my tach. Up to now, I've relied on my old 60's vintage dwell/tach. The tach hooks up to the 6/12v lead to the coil on a coil ignition. I don't want to let the smoke out of it, so thought I'd check as to whether it can be used on a magneto system.

If I had to guess, I'd try to hook the tach lead to the screw over the condenser on the mag, the one that anchors the ground lead to the switch. Is there current there that the tach can sense without grounding out the mag? Is there so much current that I'll smoke my tach? If so, any other way to hook it up, or am I gonna have to invest in another tach -- whatever they call those that sense a reflective patch on the turning shaft?

TIA

Scotty

Thanks for checking in. All I'm planning on using is the tach on the meter to adjust high and low idles, etc. There's no power at all in the tach. It's just that with the mag I don't think I have my usual low-voltage spot to hook the tach onto. UNLESS its the ground-wire stud. But I'm wondering if the current running through the tach to ground would be enough to ground out the mag, leaving me with RPMs of zero, a state I can detect quite accurately by ear. ;8^)

Setting up and timing the mag and the point gap I'll do by hand.

Set the mag statically and you are ready to roll per factory specificaitons.

I guess if you were trying to alter the mag you might need one but if you think the mag is not working take it ot a good mag shop and they will check it out and make sure the impluse coupling is working right.