I have a tach that I bought 13 years ago that mounts on the column. The only identification on it says 'Engineered in Japan'. There are 5 wires coming out of it.... 2 red, 1 black, 1 yellow, and 1 blue. One of the reds goes to the light, the other to the housing so I've figured that they go respectively to ignition and ground. Anyone know where the black, yellow, and blue ones would go?

Just a guess without the instructions; black-ground, yellow-positive for lamp, blue-distributor or coil depending on your set-up.
Jim

Sorry, I said the ignition for the one red wire, when I meant to say it was for the lamp. So, I've got a red wire for the lamp, a red wire for ground. The other 3 disappear inside the housing, so are the ones that will make it work. The black wire was cut short, like the red-ground one, so probably is also a ground wire. That leaves me with yellow and blue.

I have a stock ignition system. I expect one of these should go to a positive connection, the other to the coil. Do you think maybe they should go one on each side of the coil?

Yes, that sounds right. Yellow is usually postive. This reminds me of those "de-fusing a bomb" movies.
Jim