"Generally there are several areas for voltage drop. The drop you posted for the alternator stud is not bad at all. So the charging path is basically.........
Alternator stud........wire terminal.........bulkead terminal.........to welded splice (under dash harness in black wire)...........continue to ammeter............ammeter wire terminal............through ammeter..........ammeter wire terminal..............out big red wire.............back out through bulkhead.............fuse link and splices...........starter relay "big stud".............to battery
So each one of those points is a place for voltage drop on a stock car, and there of course can be more than one, and they add up. When you decide you have too much, you "simply" start going through the system with a meter to find it. "Let's say" in your test you had 2.4V instead of .4. To find that "Rig" some long leads on your meter for at least one probe. There are several ways to do this You can measure "to ground" and subtract voltage readings or you can measure "drop." You can put one probe onto battery PLUS post and track through the harness. Check where you can reach, at the ammeter, both terminals, at the interior side of the red and black wires for the bulkhead, and at the engine bay side of the bulkhead.
YOU MUST DO THIS IN THIS PART OF THE SYSTEM with a heavy load so to cause the alternator to be charging heavy, that is what causes the drop, is the CURRENT going through the wire. So you need, say, the engine running, the lights and heater blower running, etc
You simply compare readings. If you measure the black wire (charge wire) at the engine bay side of the bulkhead and at the interior side of the bulkhead, and get a reading of say, 1.5V difference that is a LOT OF DROP through a bulkhead terminal and it needs replaced
OTHER DROP: The ignition supply power, I often call "ignition run" or IGN1 is also a drop problem as this causes OVERcharging because the voltage regulator "thinks" that the battery voltage is low....because of the drop
This path......on a stocker..........is battery..........starter relay stud.........fuse link..........through bulkkhead on BIG RED.........to and through ammeter..........out on BIG BLACK..........to welded splice where it branches off to headlights, ignition switch, etc.................
through the ignition switch connector.........through switch........back out connector on (usually) dark blue IGN1 "run".............out through bulkhead connector into engine bay.........and branches off to feed VR, ignition system, electric choke, etc.
IF THIS PATH has poor connections, it drops the voltage to the voltalge regulator, and the regulator keeps ramping up battery voltage until the terminal (which is dropped) at the VR meets the VR setupoint. By this time the battery is OVER voltage
Finding it, same idea as the charging path
