[77 Big 10]

From your description, it sounds like only a little power from the battery is getting to the starter and then on to the rest of the system. Since the battery is good, there are only a couple things that would keep the systems from getting energized. The cables bring the + & - to the rest of the electrical system. The positive goes to the starter, and from there to the other systems. See if it is tight. But just as important is the ground. So that is where I'd look second. Clean all paint, rust and grease from a spot on the block, cable end or bracket bolted to block. If you choose a bracket, remember to clean all contact points between the bracket and block, and where you are going to bolt the cable. The starter is bolted to the block, so the ground should bolt directly to the block also, if possible. Good luck