Most electrics gone AWOL

[morph]

Hi folks, I've just aquired a 2005 (Mk2) 1.9 non turbo van, thats been passed to me as its lights, wipers, rev-counter, heater fan motor and radio have stopped working, just after its previous owner pressure washed the engine. It sounds like a BSI problem, but given the circumstances I'm suspicious of the BSM/Engine fusebox. I believe the power supply to the BSI and various other items go through this. Am I correct thinking there is a PCB below the fuses?
I presume I should have 12v on one side of the fuses and this is where I should start my checks?I assume I should check for any water entry around the BSI in the cab?
Any advise or thoughts would be greatly appreciated