P38 screen wash problem, m.o.t. tomorrow!

Any advice/experience appreciated... going in for m.o.t. tomorrow and like a pillock I've kept putting off fixing the screen wash problem... Front and rear wipers work normally, but pressing the front or rear wash/wipe button on the wiper stalk results in no noise from any of the 3 washer pumps (h/lights on or off) and no wiper movement, front or rear. No voltage is reaching the pumps. The fuse for the system is fine. My mechanic says he will try to sort it before the test, but I was hoping to get some pointers for him.

Wiper stalk switches, can the contacts go dead, can they be cleaned?

BECM problem ???

Like I said, any advice appreciated...

Just thinking, fuse box corrosion or relay maybe??

Ho well, taking it to garage now, fingers crossed..