This happened on my taz6 recently, so i feel your pain. First, the red led is wired into the mosfet circuit that drives the heater. If the bed is trying to get to temperature it will be solid. (At least mine is).
So it looks like your bed is trying to heat (Mosfet is on), but its not Getting current. Often, this means a break in the current path between the board and the bed due to a shorted connector, a wire that has broken due to repeated flexing, a connector that has become loose, or even possibly a problem with the bed heater. You need to test for continuity between the bed and the board in steps to determine where the break is, and then fix as needed.