have 03 gmc 2500 with western ultra mount. has 3 port iso module. plow has been on this truck only and was installed by a dealer. truck headlights operate as normal. plow running/turn signals work as normal. first driver side low beam was not working. no power. checked wires to the iso and nothing coming from the iso. while was messing with it iso started clicking rapidly and would all the lights off. still no driver low beam, now i have no pass high beam. what is the best way to test the iso? been reading threads everyone says these dont fail. also all other threads mention people swapping between trucks. not the case here.