Thanks for the reply ChevyTech. I removed a dual battery block and used my '90 k1500 as an example. The '90 only has one wire at the alternator connector. The '88 had 2 wires with one going to the dual battery block, I simply cut it out so it's wired like the '90. I'll connect that other wire, I think it's the voltage sense according to this post:
https://67-72chevytrucks.com/vboard/....php?p=8154775
After I get the alternator working, I'll get the truck up to temp and take some more readings.