While changing battery in a 1998 jaguar XJ8 I accidentally attached the battery in reverse, but quickly removed the wires, the horn and windshield wipers went off during the time it was connected. When I connected the battery properly, smoke began coming from under the hood. Any ideas on what have might happened!?

 

Ouch! Welcome to the forum...

It's impossible to list out every single component that could be damaged by the reverse polarity...

Probably the alternator, quite likely a number of electronic systems (including the ECU, and other $$$$ modules), also the main "mega" fuse, maybe the starter motor, all sorts...

You need to get onto an Auto Electrician who knows these cars, because it's not exactly a small problem now...