A LANCAIR 4 IN CLB AT 7000 FT DIVERTED DUE TO STABILIZER TRIM RUNAWAY NOSE-UP. CAUSED BY INCORRECT WIRING BTWN THE AUTOPLT AND THE MANUAL TRIM SYS WIRING.

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UPON CLB; ELECTRIC TRIM MALFUNCTION CAUSED THE TRIM TO RAPIDLY MOVE TO A FULL PITCH UP STATUS. SIGNIFICANT FORWARD PRESSURE WAS NECESSARY. ASSIGNED ALTS AND VECTORS WERE DIFFICULT TO MAINTAIN. PLT WAS ON PHX DEP WHEN THE PROB WAS ANNOUNCED AND A REQUEST FOR RETURN TO SDL WAS MADE. PLT WAS ABLE TO SUCCESSFULLY LAND THE ACFT AT SDL WITHOUT INCIDENT. THE MECHANICAL PROB HAS BEEN EVALUATED AND APPEARS TO BE A MALFUNCTION OF THE INTERFACE BTWN THE ELECTRIC TRIM AND AUTOPLT. MODIFICATION TO THE SYS IS BEING MADE TO PREVENT A REPEAT SCENARIO. ALL PREFLT AND PREFLT CHKLIST ITEMS WERE OBSERVED. THIS EXPERIENCE HAS CAUSED PLT TO REVIEW AUTOPLT AND TRIM ELECTRICAL SYS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE AIRPLANE WAS A HOMEBUILT KIT LANCAIR IV. THE RPTR SAID THE STABILIZER TRIM IS OPERATED BY A SINGLE MOTOR SERVO THAT IS OPERATED BY THE AUTOPLT AND THE MANUAL TRIM. THE RPTR STATED THE CAUSE OF THE RUNAWAY TRIM WAS THE WIRING BTWN THE INTERFACE OF THE AUTOPLT AND THE MANUAL TRIM CTL. THE RPTR SAID THE WIRING HAS BEEN REPLACED SEPARATING AND ISOLATING THE CTL FUNCTIONS. THE RPTR STATED THIS AIRPLANE HAD BEEN FLOWN FOR SEVERAL YRS WITHOUT EXPERIENCING THIS PROB.