AN MO20 PLT TAKES HIS ACFT FOR A TEST FLT AFTER HAVING THE GEAR WARNING HORN SOUNDING OFF WHILE TAXIING ON THE RAMP.

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I RECENTLY HAD A NEW AUTOPLT AND STORMSCOPE INSTALLED IN MY MOONEY 201J. I WAS ADVISED BY THE AVIONICS SHOP THAT THE PLANE WAS READY TO BE TEST FLOWN. THEY STATED THEY WOULD NOT BE ABLE TO PROVIDE A PLT AS THEIR INSURANCE WOULD NOT ALLOW IT. I THEN WAS TO BE THE PLT AND THEIR A&P WOULD FLY IN THE R SEAT TO CHK OUT AND ADJUST THE AUTOPLT. I DID RECEIVE LOGBOOK STICKERS INDICATING THE WORK WAS COMPLETED WHICH I PLACED IN THE AIRFRAME LOG PRIOR TO FLT. ON JUL/THU/98; AT APPROX XA00; WITH THE AVIONICS SHOP'S A&P IN THE R SEAT; I TURNED ON THE MASTER SWITCH TO START THE ENG AND THE GEAR WARNING HORN SOUNDED. THE ANNUNCIATOR PANEL WAS ALSO TOTALLY DARK. I SHUT OFF THE MASTER. THE PLANE WAS THEN PUSHED BACK INTO THE HANGAR WHERE 3 MECHS WORKED ON THE PLANE FOR 3 1/2 HRS TO CHK OUT THE ELECTRICAL CIRCUITS. THEY STATED THAT A PLUG WAS LOOSE WHICH THEY TIGHTENED. THEY THOUGHT IN ADDITION A PIECE OF WIRE CLIPPING FELL ACROSS SOME TERMINALS SHORTING THEM OUT. THEY THEN SAID THE PLANE WAS OK TO TEST FLY. I; AGAIN WITH THE A&P IN THE R SEAT; TURNED ON THE MASTER. THE LNDG GEAR LIGHTS WERE OK; AND THE GEAR DOWN HORN WAS OFF. WE TAXIED FOR TKOF. PRIOR TO TKOF THE GEAR HORN AGAIN SOUNDED. THE A&P AND I DISCUSSED THIS. HE STATED THAT THE HORN WAS ON BECAUSE THE MANIFOLD PRESSURE WAS LOW; AND IT WAS SAFE TO FLY. AT APPROX XE30 WE TOOK OFF AT GRR ON RWY 35. WHEN THERE WAS NO MORE USABLE RWY I PLACED THE 'LNDG GEAR CTL SWITCH' IN THE 'UP' POS. SHORTLY THEREAFTER THE TWR CALLED TO SAY THAT THE GEAR WAS STILL DOWN. SINCE THE GEAR WOULD NOT RAISE; I DECIDED TO TERMINATE THE FLT. AT THIS POINT THE GEAR DOWN AND THE GEAR WARNING LIGHTS WERE ON. THE GEAR WARNING HORN WAS OFF. THE 'LNDG GEAR CTL SWITCH' WAS RETURNED TO THE DOWN POS. BOTH THE GEAR DOWN AND THE GEAR WARNING LIGHTS REMAINED ON; AND THE GEAR WARNING HORN WAS DEFINITELY OFF. THE FLOOR GEAR DOWN INDICATOR SHOWED THAT THE GEAR WAS DOWN. IN CONSULTATION WITH THE MECH; I THOUGHT IT WOULD BE SAFE TO LAND. I DID NOT RUN THE 'FAILURE OF LNDG GEAR TO RETRACT AFTER TKOF' CHKLIST AS MY INTENTION WAS TO KEEP THE GEAR DOWN FOR LNDG. I INFORMED THE TWR OF MY INTENTIONS AND REMAINED IN THE TFC PATTERN. I DECLINED EMER LNDG. ON LNDG THE PLANE PULLED TO THE R AS THE R MAIN GEAR COLLAPSED. INITIALLY I WAS ABLE TO MAINTAIN DIRECTION WITH FULL L RUDDER AND FULL L AILERONS. AS THE PLANE SLOWED; THE R WINGTIP DROPPED AND I COULD NO LONGER MAINTAIN DIRECTION. THE PLANE SKIDDED OFF THE R SIDE OF THE RWY AND STOPPED IN A SHORT DISTANCE. IT APPEARED THAT UPON LEAVING THE RWY THE L MAIN GEAR AND THE NOSE GEAR COLLAPSED. THERE WERE NO INJURIES; FIRE; OR SERIOUS DAMAGE. UPON INSPECTING THE FUSE PANEL FOLLOWING THE FLT; I FOUND THAT THE 'GEAR CTL' AND 'GEAR WARNING' CIRCUIT BREAKERS HAD POPPED. I DID NOT PULL THESE. I KNOW THEY WERE BOTH IN PRIOR TO FLT; AS I HAD CHKED ALL THE CIRCUIT BREAKERS. SINCE THE GEAR WARNING HORN WAS ON PRIOR TO TKOF; THE CIRCUIT BREAKERS MUST HAVE BEEN IN AT THAT TIME. LESSONS LEARNED WERE TO NEVER FLY A PLANE WHEN THERE IS ANY DISCREPANCY; EVEN IF THE MECH SAYS IT'S SAFE. I WILL ALSO NEVER FLY A PLANE THAT HAD ANY WORK DONE ON ITS LNDG GEAR SYS WITHOUT FIRST TESTING THE GEAR ON JACKS.