What was found
(CAN) IN FLT, A/C EXPERIENCED "SHOWER OF SPARKS" EMINATING FROM L OWER INSTRUMENT LIGHTING DIMMER POTENTIMETER. DURING APPROACH PILOT TRIED TO ADJUST THELOWER INSTRUMENT DIMMER THESPAR KS FLEW UPON LDG.THE INST WAS INSP/IT WAS NOTED THAT SOLDERED CONNECTION OF BOTH UPPER & LOWER INSTRUMENT DIMMER POTTS WERE CONTACTING EACHOTHER. SINC E THERE IS NO POSITIVE ENGAGEMENT OF POTENTIOMETER TO INSTRUMNET PANEL. IF ATTACH NUT ON POTENTIOMETER BECOMES SLIGHT LOOSE, POT ROTATE & CONTACT ADJACENT POT. BOTH POTENTIOMETERS WERE RE-SECURED IN ASAFE POS AND CHECKED FOR CORRECT OP/OTHER DAMAGE TO SYS. FLEET CHECK. ONLY ONE OTHER A/C HAD A LOOSE POTENTIOMETER.