‘87 V20 Alternator / Battery Wiring - Will not charge!

[FoxCustom]

Hey guys,
While cruising home on Friday night, I notice the voltage gauge drop to around 10 volts and all the lights go dim. Made it home fine. Swap in a new (remanufactured) NAPA alternator on Saturday with no luck - no charge, nothing. The truck is just running off the battery - just 12 volts.

Does this wiring arrangement look correct?? I’m not quite sure what the blue aluminum heat-sinked block is up on the firewall?? Any ideas what else I could check?? Fuseable links?? If it were a fuseable link, would I still be running off the battery or would the entire truck be powerless??