main thing to do to isolate the problem is putting a test wire into the solenoid wire ( solenoid switch terminal) with the test light connected , clamp on the neg battery, crank the engine and let the engine idle . if the light stays on , you must have an electrical problem . but if the light goes off and you feel that the starter is still engaged, that must be the starter itself.

if it's electrical , you must need a diagram for starting systems handy .