[longdistancerider]

Green is Ground. Black is switched power from the ignition switch. If there's Black and Green connected then the Black wires were added by the PO since the harness hasn't melted down when the key was turned on. Need to removed the tape on the harness and figure out what the PO was trying to do

 

[longdistancerider]

The splices in the picture are original Honda.
There's a second small wire coming off the solenoid, Green w/Red. That is the ground circuit for the solenoid and is connected to the neutral safety switch and clutch safety switch. You can check that there is ground by using one VOM lead to the positive battery terminal and the other to that wire connector. You should see ground/voltage reading when the transmission is in neutral or if in gear when the clutch lever is pulled. There is a "rectifier" in the circuit to prevent voltage feedback because of the 2 different type circuits. If that diode is missing the starter won't work in neutral.

 

[longdistancerider]

Your ground readings are fine.
With the trans in neutral, use a jumper wire from the positive battery terminal to the Yellow w/Red wire connector by the solenoid. If the starter works the solenoid is good. Now use the same jumper to the Yellow w/Red wire in the connector at the headlight. Starter works? If so then connect the jumper wire to the solid Black wire in that same connector and try the switch. Starter works? If so the use your VOM to check for voltage on the Black wire with the key in the ON position. If the starter doesn't work on this last test then the switch is bad