Ross, maybe in a couple weeks, I'll see if the function generator is still in the closet, find that tach amp that I bought, and see if the Maserati tach I bought for whatever reason (I think from an Indy...what a lovely thing and the same physical size as the Goose/Pantera tach) actually works.
Since we're both electronics folks, I'd be curious if the MSD needs an external pullup--at least, it would have been a really safe thing for MSD to just have an open-collector output so somebody connecting anything wouldn't damage the output... but probably, we just don't need to know Lee