I'm not so sure. Maybe I should have been a bit clearer in my OP.
They have been working fine until I gave it a wash the other week (pressure washer, snow foam etc).
Since then sometimes none work, sometimes only as little as one quarter. They seem to work most of the time, but I'm just worried I might have drowned one or two of them!
To be clear, the front and rears are 100% working.