During cruising flight the pilot noticed an indication of a high battery discharge rate, and saw that the alternator and landing gear pump circuit breakers had popped. Both breakers were reset, but a short time later the gear pump breaker popped again. The pilot reset the device and shortly afterwards smoke was observed coming from the centre console area. The pilot elected to make an immediate landing on a short, disused strip. The aircraft overran the strip and the pilot steered the aircraft into a tree to avoid running into a gully. An internal fault in the landing gear hydraulic pump resulted in damage to the pump motor, which then ran continuously, overloading the circuit. The resetting of the circuit breaker allowed the overload condition to continue until the over-heated powerpack venting system failed and hydraulic oil was sprayed over the unit, producing the smoke in the cockpit. The pilot subsequently misjudged his approach and touched down half way along the selected strip.