Q: RV won't say a word but headlights come on

I have an 1988 Coachmen Catalina on a chevy van chasis v8. When I bought it the guy put a new starter, solenoid, and battery on it. He also changed a few fusable link wire. I let it sit over the winter and only started 2-3 times to check that it started. The choke light came on. I never fixed the choke or timing so it idled fast. Finally I drove it to work one time. On my way home I put some Marvel Mystery Oil into the gas tank and fueled up. The darn thing wouldn't start. I got towed home. I checked the starter wire and reconnected it. While unhooking the starter at first I forgot to disconnect the battery and the blasted thing kept turning on in my hand until I moved it away from metal parts. So I know the starter works. I reconnected the wires and hooked it back up. I then tested the solenoid. When I took the wire off the right small terminal and touched it to the left terminal I got a buzz sound. I got the battery charged. Still nothing. What gives?