76 Plymouth Valiant won't start

Just got back from a test drive. I started to take the battery cables off and though to try to start it, "just for ***** and giggles" and it started right up, by jumping it across the relays. killed it and started it with the key... Drove it about 4 miles round trip and came home, killed it and started right back up...

While I was driving, with my foot in it, the speedo jumped up to 70 and went almost to 90, before I slowed down. It went to zero when I stopped at a light and then went up to 10 when I took off and sat at 5 when I was in a 35 zone, trying to blend in with traffic...

Now I need to go ahead and recheck the battery cables and connectors and take those felt gaskets off and put some grease on, then fix those two wires...