John, The 13.7 volts was probably without any current being running in the wires. The voltage on the solenoid terminals when the starter systeme is energized is the essential thing. There may be substantial voltage drops on "bad" connections, necked down wires at connections, etc. The starting solenoid windings could be old, and partially shorted out due to bad insulation on the wires. This would result in less pulling power by those windings. There would be older grease, that is more viscous (tackier) so it takes more pull by the windings to move the solenoid, and starting gear system. With less pull, and more requirement for pull, the system won't work. You may find some great information about starting systems in your public library for automobiles, which have similar electrical starting sytstems. Bob C27 #3587
