1983 dodge d150 overcharged battery

It depends on what is causing the drop. In other words, where is the resistance? If its in the ignition circuit, then the relay is a decent solution. If its in one of the power feeds, then IMO it is much better to fix the power feed. This all makes the assumption that the '83 D150 is wired with a main splice under the dash where the power feeds all join.

It's also possible the alternator field to regulator wire is grounded (pinched or brush terminal insulator missing)

To find the where the resistance is.
Before doing this, slow charge the battery if its low.

1) get a wiring diagram, and/or look over your vehicle to see if the battery line, and the alternator output go through the firewall and join with the circuitfeeds under the dash. I think trucks still were wired like that in 83 but dont know for sure.

2) Engine off, measure voltage at battery and at alternator output. Should be the same. Should be at least 12.5 Volts.
+ turn on lights, read ammeter, and check the voltage at the battery positive and the alternator output. Then do a direct measurement of the votlage difference between the battery positive and the alternator stud. That's the voltage drop in the battery line to the main splice for X amps (whatever you read on the ammeter).
If there is a voltage difference to ground that is more than the direct voltage drop measurement, then there is resistance in the grounding.

3) Engine running. Read the ammeter. Measure the voltage at the alternator output, the battery positive, the regulator input (ign terminal).

The voltage at all three should be the same. Voltage differnces between the alternator output and the ign terminal of the regulator indicate resistance between those two points. If the alt and bat voltages are the same, then the faults are probably downstream of the mainsplice. If the alt and bat voltages are different, then depending on the ammeter reading - we can estimate how bad the resistance is between those two points. If the battery feed to mainsplice was OK in the headlight test - engine off, then the fault is in the alternator's output wires and connections. That must be fixed.