Charging issues?

Any "good" parts store should carry these solenoids, just make SURE it is continuous duty. They are used in motor homes, etc for dual battery hookups. STARTER solenoids won't work--the coil will burn up in about 15 minutes.

Not knowing how your wiring is hacked, I'd just trace back the regulator "I" (ign) terminal and the blue alternator field. Both of them should go to the same place --the "Y" off to supply the ignition system. So you need to isolate those three things at least, and put them on the cold side of the relay/ solenoid. The wire should continue on through the bulkhead back to the IGN switch.

You don't absolutely HAVE to use this solenoid. You can break the alternator field, OR the ignition field with a smaller relay the way you tried to earlier. I don't think it matters which field wire you break, or you can break the "I" lead to the regulator as well. Any of these points will kill the engine when the disconnect is pulled.

14.9 is a little high. You may be suffering "voltage drop" to the "I" terminal on the regulator. On a factory - wired car, this circuit path is

from the battery -- starter relay stud -- fuse link -- through the bulkhead -- ammeter circuit -- in harness splice and to the ignition switch connector -- through the switch -- back out the switch connector --(on the dark blue IGN run) -- back out the bulkhead -- to the IGN system, alternator field and regulator

Your top suspects for v drop problems are the bulkhead connector, the IGN switch connector, and the switch itself. Any bad connection in this path supplies LOW voltage to the IGN/ regulator circuit, and the regulator compensates by ADDING that voltage to it's set point, thereby causing an overcharge condition.

If this IS the cause, it means your IGN system is getting starved. Changing to a solenoid is ONE way around this problem, IE getting the supply voltage under the hook closer to the battery.

Make sure you have good, big jumper grounds between the engine and body, and good cables on the battery.