I have a 89 frod f250 but the original owner has

I have a 89 frod f250 but the original owner has replaced the motor with a 351. I was gopin to get it tagged yesterday and when i was driving it home,I lost power slowly until the truck went completely dead. I finally got it started, after i had the battery completeely charged at Auotzone, I was able to drive it home but smelt a wire burning on the drive and my battery light came on when i pulled in. I was only able to get the truck started by putting a screwdriver across the opoints of my new selonoid. Please help