Need a little more info: (running like total asshole says nothing)
1. First off, I'm assuming this is a GS-T or GSX (year ? )since you say it sounds like its running an open downpipe?
2. Is it running really rough? Describe it
3. So you're saying it ran fine until you changed the plugs and wires?
4. What kind of plugs did you buy?
5. What kind of wires did you buy?
6. Are you 100% sure you have the wires in the exact order they should be? If so, go recheck them again. If you're not sure, I'll try to give you the order they should be in.
7. What caused the injector wires to melt?? There has to be a reason.

Just for starters. From there, people may be able to help you