ACFT EQUIPMENT PROBLEM.

Narrative

I WAS ON A DAY CAVU TRIP TO A DEST OF ABOUT 115 MI. THE ROUTE WAS ALMOST FEATURELESS; BUT LAY BTWN A HWY AND THE GULF OF MEXICO COASTLINE; ABOUT 20 MI APART. THERE WAS NO WAY TO MISS MY DEST; BUT THE SITUATION WOULD APPLY IF ON A MARGINAL DAY TRIP OR AT NIGHT. I WAS USING MY NEW HANDHELD NAV COM; AS MY COM SYS HAD BEEN REPAIRED; REWIRED AND REARRANGED LATELY. THE COM DIDN'T WORK. I HAVEN'T GOT THE OPERATIONAL SITUATION WORKED OUT YET; AS WHERE TO PUT THE UNIT WHEN NOT IN USE. I FOUND THE BEST PLACE FOR REACHING IT AND RECEIVING SIGNALS; TO BE ON DASH IN FRONT OF THE WINDSHIELD; WHICH IS NEAR MY COMPASS MOUNTED ON CENTER POST. I GOT THERE OK; NO PROB; AND WAS RETURNING WHEN I NOTICED THE HDG FOR DEST WAS 15-20 DEGS TO E OF COURSE. THIS SITUATION WAS VERY OBVIOUS BECAUSE OF MY GUIDE LINES ON EACH SIDE OF COURSE. IF THE ROUTE WAS LESS OBVIOUS OR IN BAD VISUAL CONDITIONS; THE DISCREPANCY WOULD NOT HAVE BEEN NOTICED; AND I WOULD HAVE THOUGHT MY INACTIVITY LATELY WAS LETTING MY HDG WANDER; CAUSING ME TO RESET MY DG. ON USING AND REPLACING THE HANDHELD; I SAW THE COMPASS PROGRESS TO THE RIGHT. AS I MOVED THE UNIT FURTHER FROM THE COMPASS; IT CORRECTED THE ERROR. SLIDING IT TOWARD THE COMPASS SHOWED A PROGRESSIVELY GREATER TURN TO THE RIGHT OF CORRECT POS. THIS IS A STRONG REMINDER TO NOT DO ACTIONS DIFFERENTLY IN OTHER THAN USUAL SITUATIONS. DON'T CHANGE THE POS OF FLASHLIGHTS; HANDHELDS OR HEADSETS TO DIFFERENT LOCATIONS BECAUSE OF LOW VISIBILITY; NIGHT FLYING OR MECHANICAL PROBS. BEFORE ENCOUNTERING SUCH PROBS; DECIDE WHERE YOU WILL NEED TO POS ALL ITEMS THAT MIGHT BE NEEDED IN ADVERSE CONDITIONS; DECIDING DURING GOOD VFR FLTS.