[LH Lead-Foot]

What Ray said is the best way to get started as there is considerable amperage going thru the PPL wire to the starter solenoid. Don't forget to look for loose or burn't terminals like the one behind the fuse box. This is the male to female plastic connector that may result in terminal push-out causing loss of voltage. The metal terminal is only held in by a small metal tang that locks it into the plastic connector. So, past repairs or pulling on the harness could cause the terminal to pull apart enough to create resistance to cause your loss of voltage.

The 12 AWG RED wire to the ignition switch is battery hot, so with a decent digital volt/ohm meter, it should be current battery voltage. Try it with head lights on, blower fan on high and wipers. A small amount of voltage drop or loss occurs in connectors and the length of wire, but should read real close to the battery with things turned on.

The PPL starter solenoid wire supplies current to the pull-in coil of the starter solenoid and the holding coil at the same time when cranking. Once cranking, the pull-in coil becomes de-energised once cranking begins. The solenoids movement alone completes the large amperage switch inside to connect the battery with the cranking motor. At this point, the solenoids amperage draw drops lower.

Best of luck and let us know what you found.