So, like a lot of other cars, the stock tach in my '91 doesn't work. Instead of purchasing a whole new cluster, I just bought an autometer aftermarket tach. I have 2 main questions to ask about it.

1. It says to wire two separate wires, one to the battery and one to the dash lighting. However, I plan on using an add-a-circut to do this. If I wired one to the dash lighting fuse, and other to a switched 12v, would that work? And which one would I ground to?

2. Could I just connect the tach wire to the stock wire inside the dash? If not, where would I connect it?