The signal is consider floating when it does not have the same ground with your device. Earth has nothing to do with it. Earth is just another ground.
earth on a moped is the frame.
nice article but this one c/p says it.
big diodes exist but are silly expensive. if you want a 25a diode you run the kbpc5010 bridge half wave leaving the negative terminal unconnected. this part only costs a buck.