14.6 volts looks like a "rapid charge" mode from the converter. It enters to the mode when the battery
voltage is too low. Maybe the battery is dying? Get it checked. Also could be defective LEDs, like the most sold
on ebay for cheap. Actually they are not defective, but are designed to work in car's turning lights
. The symptoms are - when turned on it lights
bright, but after a few minutes becomes dim, colour becomes blue-ish and the LED "bulb" becomes very hot. Been there, know that...