I have just had the engine out to change the clutch. All back in but I have an electrical problem. the starter motor doesn't disengage when the engine starts. Took start off and operated it, works fine. On releasing ignition switch starter stops. I put it back on, disconnected spark plus, all OK, engine turns and stops when key released. Soon as it is bolted on and engine starts it keeps running? Must be something I have got wrong on the wiring. The only other wires which have come off are the alternator. Could I have crossed wires somewhere? On the alternator is the light wire fixed to the lower terminal?