Single wire alternator not charge

[lukbrw]

Looking to get some advice on a charging system. previous owner did the single wire upgrade to the 64 c20 that we picked up. All the wiring looks correct and there is a resistor under the dash that is lighting up with no issues. Everywhere we test we only get 12.4v going back to the battery.

Replaced a few ends and cleaned up the terminals but no change.

Alternator was bench tested at Oreilly's with no issues.

Brown, blue, and white wires that went to the old external regulator are not connected to anything as described in previous posts.

We put in a new battery, but the old battery had the same amount of voltage.

Any suggestions on something that needs to change or check?

Thanks!