computer problem?

[87mustang]

hey, i have a couple questions for answering (desperatly). I changed my heatercore (nightmare of a job) and during trying to put everything back together i found two female plugs behind the stereo area. Then found another set of male plugs, one pair looked asthough they went together so I plugged them together and put everything back together and my fuel gauge doesn't work now and the interior lights don't work, so i found that i blew a 15amp fuse (no.8 fuse). Stupidly i put a 20 amp fuse in instead and something on the righ side of the dash clicked or popped and the car started idling rough and didn't want to stay running and burning very rich.(ouch!) Could i have killed the computer or burnt out a possile performance chip that may have been installed before i got the car? And what is the difference between an "ecu" and the eec-iv,which one is possibly bad? Please help, i don't like not driving this car!