'64 dart amp gage

i'm sure the M.A.D. conversion is my next step, but here is what I find. good battery fully charged, I have done this with 2 good used alt. one single field, the other square back 2 field alt. ( with second field connection grounded).... after the engine is warmed and battery settled. the v, will read basically about 12.1- 12.2 at alt. and batt. at idle, and reved up about 12.6 at both alt. and battery. the VR shows about 1 v. drop from what I read at batt and alt, losing current inside dash I guess? when cold the idle v is 13 and drops as it warms.

NOW, at idle , inside , the old amp gage shows right in middle between C and D, but when reved it clearly shows discharge. the car idled maybe 20 minutes but the battery never showed any sign of running down, when I pout the charger on it.

car is not yet insured but I did drive it down our back roads 2-3 mi. ran good, no problems surfaced, but since no insurance I did not want to drive further.

this 64 dart has the stud connection at the bulkhead instead of the common wires into the plug deal. I have been told those pose fewer chance of problems, but no doubt the MAD change would be wise. question is, why does the amp gage show this discharge?????? bad gauge or connections.