Installing a Tachometer in a 73-79 Ford Truck

I recently picked up a 1977 F150 for pretty cheap. It had a tachometer on the dash but I noticed that it wasn't working. I decided to dig in to see what was up, since it looked like it was wired up already. I ran into a few surprises but nothing that couldn't be undone. I've seen a few people ask from time to time how to hook a tach up, so this procedure should be the same for just about any Ford truck made from 1973 to 1979.