The wiring is there in your truck. For your '88 look for a single red wire with a black(?) flat connector around the collant bottle. You will have to modify the light if it has the two wire connector. You could grab the harness portion from the yard and attach your red wire to it and ground the other wire if you don't want to cut the connector off the light.
The wiring is different between '89 down and '90 up. For '89 down there is a single wire, the light grounds through the mounting bar. For '90 up there is a two wire connector.
Here are some threads with pics of the frame.
https://comancheclub.com/topic/152-removed-the-bed/
https://comancheclub.com/topic/21066-long-bed-stuff/
https://comancheclub.com/topic/55204-bed-bolt-locations/?tab=comments#comment-564686
https://comancheclub.com/topic/15384-quick-bed-removal-problem/
I have three and the funny thing is my neighbor directly across the street also has one, we've been neighbors for 24 years! I've been meaning to post it's VIN since I don't think she's on here.
It looks like fewer were made in the 90-92 model years. If our registry is an accurate snapshot of the relative number produced by year, peak production was '88 and '89.