Originally Posted by Sergeant Joe
The fix is to run an Earth wire from Neg side of Dioad board through to the bolt that holds the back of the starter motor to the engine case.
Makes no sense to me that since the starter grounds through the engine block at it's mounting point. Can't get much better grounding than that!
The best test for the starter (with a known good battery) is to hook jumper leads directly to the starter while it's installed.
Run the negative jumper from the battery negative to the engine block near the starter.
Connect the positive lead to the cable mounting lug on the starter.
Jump 12V to the solenoid spade and the starter should spin the engine.
If it doesn't, something aint right with the starter.
It's possible to have a poor connection in the solenoid contacts.
Often it's worn bushings in the starter - there are three - two for the armature, one in the bendix drive.
Or it's brushes and grungy commutator.
If the starter turns when the button is pressed, it's not the relay - since that's what the relay's function is - to activate the starter.