Started a small fire replacing battery

I have an old school 1978 Ford Econoline 150. I'm pretty sure the engine is the 351 V8. The battery died the other day, and I bought a new one. Not the same size as the old one (smaller than the old one), but had better cold cranking amps, so I picked it up. I had to replace the positive (red) battery terminal, as the bolt was corroded. I put the negative terminal on first, and then touched the positive terminal, and big sparks were coming from the terminal. I tried switching the sequence, and a small fire ran down the length of the negative terminal, and now the van won't crank. I don't know if it was the battery, or what the deal is/was. Any suggestions? Nothing is turned on, such as lights, or other accessories, as this van only has two captains chairs, and an empty cargo bay. Thanks for your suggestions.

you have a dead short from positive to negative on the van.
Hook an ohm-meter to the positive and negative cables that would go to a battery without a battery on there and you will see that must be true in order for a fire to be started and the sparks as you mentioned.

You are very lucky, given your description of the problem that the battery did not explode and injure you.

you have a dead short from positive to negative on the van.
Hook an ohm-meter to the positive and negative cables that would go to a battery without a battery on there and you will see that must be true in order for a fire to be started and the sparks as you mentioned.

You are very lucky, given your description of the problem that the battery did not explode and injure you.

Appreciate the help. What do I need to do in order to resolve the dead short?

some fords used a reverse teminal battery , make sure the polarity is right .some one might have replaced the cables and changed the color