will not start?

Yes. Just think logically.
Power goes from battery, to starter solenoid, solenoid to starter motor then out of motor to chassis/ground/earth and finally back to battery.

With a test meter set to volts (or a 12v bulb even), put the negative lead on the battery negative then check volts down the chain of connections.

12v on battery + term?
12v on starter switch input?
12v on starter switch output when key/button operated?
12v on starter solenoid coil terminal when key/button operated?
12v on starter solenoid big input terminal?
12v on starter solenoid big output terminal when key/button operated?
12v on starter terminal whe. Key/button operated?

Same checks again with negative lead connected to the chassis

Think. Draw diagrams.

Skkdiud
August 2019