So, the initial drive showed a few issues. Most were simple fixes of minor things, but one major problem was a random failure to crank. I had a starter relay mounted on the fender. and from that relay a 14 gauge wire snaked down to the starter along the main battery cable, a distance of perhaps 7-8 feet total. It seems this length of 14 gauge had too much resistance and gave marginal voltage at the starter solenoid terminal as well as some heating of the wire.
The immediate idea for a solution was to run a larger wire, but that meant threading a 12 or 10 gauge wire through an already-mounted loom. Instead, I close to eliminate the relay from the fender and connect the ignition switch start wire directly to the wire going to the starter. I then moved the relay to the frame rail adjacent to the starter, and used the starter wire going to the starter to instead actuate the relay. The relay switches power directly from the main battery terminal on the starter, protected with an inline fuse, to the solenoid terminal when the key is in the start position. The wire on the fuse holder is 12 gauge, while the other wire is 14 gauge. Since resistance increases with length, and the wires are kept very short with this arrangement, there have been no more failure-to-crank issues. Here's some pics before I put convolure tubing over all the wires:
I put a reverse-biased 50V Schottky diode between the starter wire and the ground wire. When the relay opens, the energy stored in the magnetic field of the solenoid has to go somewhere. Normally, it arcs across the relay terminals as they open, which will eventually cause the relay to fail. The diode allows the reverse current to travel harmlessly to ground with no arcing, where it is dissipated as heat in the solenoid winding.
Here's the installed relay and fuse:
This setup engages the solenoid without fail, even when the batteries are too weak to give more than a half-crank to the engine. The weak batteries were caused by my alternator losing a diode, which is a story for later time
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