1988 40 HP no starter response

[AlexanderR7]

My 1988 40 HP has a rebuilt starter which cranks when 12 volts is supplied to the lower terminal of the starter solenoid. But when the ignition is turned to the start position, 12 volts shows at both control terminals of the solenoid, but starter does not crank. So I replaced the solenoid in hopes it was the problem, but after that still no starter crank.
Should one of the control terminals be a ground? What could solve this dilemma?
I did some other work on the engine - replaced thermostat and head gasket - so I may not have got all the wiring properly hooked back up; it started OK before this.
Thanks for any helpful suggestions.

[boats.net]

The yellow/red wire should have 12 positive when key is in start position, small black wire should be grounded.