I had the same problem on my Plus 4. The problem was that the 12 volt was not being applied to the starter motor solenoid. The solution was to locate the connector between the internal harness and the engine harness. Break it open, use some contact cleaner, and plug back together. In my case the connector was on the extreme right side, under the dash. I did take the precaution to treat all connectors to the same treatment. Some months later my Plus 8 developed a similar fault, again a harness connector.
