26-07-14, 10:02 PM
My point was that that may be a false positive… i.e the fault, wherever it is, wasn't exhibiting itself on those occasions. The 12v output from the relay when the motor didn't spin, on the other hand, is conclusive evidence that the fault lies downstream of the relay.
There are only a few connectors to look at, I'd be inclined to scrape and tighten all of them and if that doesn't chase the gremlins away, whip the motor out and check all's well inside. If I had to put money on it, I'd guess glazing of the armature/worn brushes is the likely culprit.