Disassembly one and post the pictures. These run on 12volts(up to 20 lights parallel to one powersupply????). So, you most likely have a resistor or driver in each light module. Either could be bad. Once you see the type of LED in there, and its circuit, you should be able to find an equivalent replacement. Double check the wiring resistance as it could be a simple corrosion problem at the wiring.
