Very difficult to find a wiring diagram for the SC Hiace. Or any Hiace
I don't think you'll damage anything if you just remove the fuses one at a time until the drain goes (use a clamp ammeter).
However if you know while solenoid it making the noise I'd burrow a bit and disconnect it - it may be that is faulty. Or is that your plan anyway?
I fitted a battery switch to mine - useful while a faff about with it. A Half-turn and it's all off, completely dead.
BTW one day I'll need to find the central locking stuff as I want to add a remote unlock/lock system, rather than having to use the key in the door.