Need help with in-dash voltmeter

[dennis1995tbird]

Need help with in-dash voltmeter.
I had valve guides replaced, now the meter is all the way down.
Battery is charging correctly and the RED battery warning indicator works.

I thought the mechanic left a plug off, but all looks normal under the hood.
I looked under the plastic air horn also.

Does anyone have a schematic showing how the in-dash voltmeter is connected?
My manuals don't have that detail.
Thanks in advance for any replies.
1995 4.6 v-8 auto, full power (windows, locks)