THE PLT MADE A PRECAUTIONARY LDG AFTER EXPERIENCING ACFT ELECTRICAL PROBLEMS AND OBSERVING THE AMMETER INDICATE DISCHARGING. THE NOSE AND RT MAIN LDG GEAR COLLAPSED DURING ROLLOUT BRAKING. THE PLT REPORTED THAT THE GEAR HAD EXTENDED PRIOR TO LDG USING THE NORMAL ELECTRICALLY-OPERATED SYSTEM, BUT THAT THE GEAR DOWN & LOCKED INDICATOR LIGHTS DID NOT ILLUMINATE; HE SUBSEQUENTLY ATTEMPTED TO MANUALLY EXTEND THE GEAR, BUT 'COULD NOT' TURN THE HANDCRANK TO DO SO. AFTER RECYCLING THE GEAR ELECTRICALLY, A TWR FLY-BY WAS MADE AND ATC ADVISED HIM THAT THE GEAR 'APPEARED' TO BE DOWN. A MECHANIC WHO ARRIVED ON SCENE SHORTLY AFTER THE ACCIDENT OCCURRED RPTD THAT THE PLT STATED HE HAD 'FORGOTTEN' TO USE THE MANUAL SYSTEM. THE MECHANIC LATER OPERATED THE HANDCRANK AND FOUND THAT IT APPEARED TO ROTATE NORMALLY. EXAMINATION OF THE ACFT BY THE FAA REVEALED THAT THE GEAR DOWN & LOCKED INDICATING SYSTEM WAS FUNCTIONAL. NO PROBLEMS WERE RPTD WITH THE REST OF THE ACFT ELECTRICAL SYSTEM.