Isuzu 3AB1 starter issues.

[DE38]

I have a DE 38 that I just bought it has a Isuzu 3AB1 and I went to start up the engine on a cold morning and it would not start, then the key in the off position the starter motor would not stop.
I turned the battery off at the main and disconnected the battery’s in the engine room and it stopped.

Could it be the solenoid?

[Lepke]

It could be anything in the start circuit, but the solenoid contacts can become pitted over time and draw more amps than their rating to make contact. More amps causes more pitting and can weld the contacts together.

Most solenoids have two copper studs, one for the battery cable and one to the starter. A disk makes contact with the studs. The disk turns slightly each use to to keep pitting to a minimum. The solenoid is an electromagnetic switch. The contacts are kept apart by spring pressure, When the solenoid is energized, the switch overpowers the spring and the disk makes contact with the studs.

If you disassemble the solenoid, the stud/contacts and the disk pitting can be filed to restore the solenoid to like new condition. On some solenoids the disk can be reversed. Cheaper/smaller solenoids have a non-rotating bar instead of a disk.