This Correct Reproduction ''front light'' wire harness for your Chevelle & El Camino is an absolute must for any good restoration as this harness includes the alternator & voltage regulator charging cicuit. The ''STOCK'' option is for cars with the original style externally mounted voltage regulator. Many enthusiasts prefer to update their car with the later GM internal voltage regulator alternator, often referred to as a ''Single Wire Alternator''. If your car is so equipped, choose option ''DRIVE INT'' for a driver's side mounted single-wire alternator, or if you have relocated it to the passenger side, choose option ''PASS INT''. It's that easy !