Fire under hood. What part is this?

[bubbalou65]

Well I got home from a long trip for work and thought I would run the truck to warm it up. Run well then died cause it was pretty cold. When I started it back up it back fired and boom big fire. I am wondering about a plug on the firewall. It is a plastic plug with 2-3 wires. It is just to left of the trans dipstick in the picture. The engine is a 1978 350. Any help. Cant seem to find it online. Thanks Well couldn't upload the pic. Think its because im at work.