Theres 2 wires with terminators underneath the seat that should be insulated from shorting out on the frame. One is for the optional rear work light (it's hot when the key is on) and the other is what lights that light when it's grounded. The European models apparantly have this HST overheat indicator but the N American market BX's do not have the sender installed in the HST, so it's not used. That connector is probably shorting out on the seat hardwarem, the frame or is wet and shorting out to the frame.
Good luck
Dave