I do have a voltage regulator mounted on the truck front clip frame. And the factory wiring diagrams show this is correct.
Also, it looks like there is a brown or brown/white wire from the ignition switch that ties in with the old brown generator light wire in the fusebox sandwich plug on the firewall.
OK, so let me clarify this. You swapped from idiot lights to factory gauges, and in order for your batt gauge to work you had to run the brown wire from the old dash clip wire #8 to the new dash clip wire #5? Because #5 on my diagram:
http://www.gmcpaulstruckparts.com/Tech%20Tips1.htm is not used (blank), just like in the idiot light dash wire #3 wasn't used.
Also, the temp gauge wire is #6 not #5, so I'm a little confused still on your reply.
Clarification requested. Thanks again!