My 88 Suburban has been fine for the last two years (reference point).

About a month ago I discovered the battery being drained.

1) Discovered Alternator Voltage Regulator was not operating.
1a) Took specs/model/serial from alternator
1b) WESTLING 71-7890-11 12V 100A 4-pin became WILSON 90-01-4182 12V 105A 4-pin
1c) 90-01-4182 - 71-7890-11 - WILSON ALTERNATOR REPLACEMENT FOR WESTLING 71-7890-11 WITH A $15.00 CORE INCLUDED IN THE PRICE - Filter Products
1d) FYI: Also tried intermediate NAPA 213-4521D 12V 100A (sanity check)
1e) Summary: Both show Charging System NO VOLTAGE

2) Discovered positive 4 gauge cable to Starter was very corroded under casing
2a) Replaced with 4 gauge cable from Battery positive to Starter
2b) Replaced with 4 gauge cable from Battery positive to Alternator
2c) Replaced with 4 gauge cable from Battery negative to Ground Plate (below Alternator)
2d) Checked and rechecked all wiring connections (newer, older)
2e) Newish battery fully charged overnight
2f) FYI: Also tried an intermediate second battery
2g) Summary: Charging system NO VOLTAGE (Battery Voltage 13.06, 832 CCA)
2h) Drain test 0.05a (to address perceived off, but live drain theories)

Quick Summary:
So basically I was running fine a month ago . . .
Replaced alternator (two), battery (two)
Replaced wiring from battery to starter (new)
Replaced wiring from battery to alternator (new)
Replaced wiring from battery to ground (new)

Two VERY strange sidebars:

3a) Dash board volt meter is not registering
3b) Dash volt meter has dropped dead below 8v (as if disconnected)
3c) Reasoning might be because of Alternator NO VOLTAGE

4a) Lights work = no issues
4b) Dash lights turned down/off = no issues
4c) Dash lights turned up/on = BUZZER
4d) Reasoning might be because of Alternator NO VOLTAGE

5) I have checked, but not replaced the smaller wires into Alternator

6) So I am driving around watching my battery loose voltage,
recharging manually (since new alternator(s) is not charging)
and dynamically tracking voltage loss with Stinger in cig lighter

The most important reference point. One month ago and for two years preceding all was well.

Need help from a techie guru . . .

 

I had the exact same issue and ultimate fix ended up being a 20A fuse. I did check all these before replacing the alternator, but before tearing apart the dash or tracing wires, I figured why not check again. I ended up finding the 20A fuse for the Gage/Idle was blown. replaced and all is well. I would like to credit my friend for his help in trying to track down this issue.