What is the voltage reading at the front screw terminal on the voltage regulator?
The battery is the main stbilizer of the alternator output. The two work as a team. In order to work in this capacity, it must have a good connection. I would start by stripping every connection between alt and batteries And confirm all the connections are clean, tight and the crimps are not corroded up into the cable… also check the connector from reg to alt chassis.
Do you know how to measure line loss/voltage drop? Long test leads on a voltmeter, and a battery load tester. Measuring voltage from one end of a cable to another by putting one lead on one end of the + cable and the other lead on the other end of the + cable. Connect the load tester to + and ground at the end end of the circuit oppisite the power source and apply ~100A of load. Measuring like this you will see the voltage dropped along the cable due to all the wiring and connector resistances. You also need to measure the voltage at the source(12 or 24V) The voltage dropped along the cable should be less than 3% of the source voltage. For example 3% of 12.5v is .375v, so a meter connected to each end of a cable should so no more voltage than that with full load being pulled thru it. a 25v circuit should see less than .75v. This test can help you to diagnose poor connections.
Any connection issues need to be ruled out efore you can look at something more troublesome.
