I have a Motorguide 768(with 12/24 switch) that quit working on 24v. My Stratos 279v has the factory wiring with 2 large A/C Delco trolling batteries in series that are 2+ years old . Both batteries have a fuse harness each and a circuit breaker on the postive posts. Fuses are in tact, batteries read green,but one of the circuit breakers does not reset(manual). It is one those small rectangle black breakers with the button. The motor runs only when switched to 12v. I realize it may be a slew of things, but maybe someone has had a similar problem. Help!  :'(

I'd say if one of the circuit breakers doesn't reset it's a bad circuit breaker.

Keep in mind that if a circuit breaker won't reset, the short or overload that caused it to trip may still be present.  This would prevent you resetting it.  Take one of the leads off it and then try resetting, if it works now you have a short or overload somewhere in the circuit.

Looks like I will disconnect the circuit breaker first to trouble shoot.  I will gather some more great ideas like yours before I undertake the task by mid-week.  thanks