There are two small wires comming off the starter motor, one of them supplies power to the starter vibrator, if there is corrosion on these connectors it will stop the starter vibrator from working. This has just caused us plenty of grief, the engine cranks over as normal and you think it has to be a fuel prob but after flattening the battery a couple of times and a couple of very puzzled engineers we found that there was corrosion on these connectors and there was no power getting to the Starter vibrator, another indication was that the starter light was not iluminating. Might be of help.