I need to change two tail light sockets in my 89 IROC z and encountered something weird. My tail light sockets have four wires. Every parts place I call has tail light sockets with only 3 wires out. Has anyone ever heard of this? Any where other than Chevy that I can get these sockets or a tail light wiring harness with this set up

There are at most only 3 contacts to any bulb; ground, tail, brake/TS.

If there are 4 wires going to a bulb, then at least 2 of them are going to the same contact, and can be spliced together and to the proper wire of a replacement socket.

GM light circuits ALWAYS use colored wires. You can figure out which wires are which by simply looking at the colors.

You can get sockets that will work just about anywhere.