Washer Wiring - Troopy

Hi Folks,

Ive only recently bought a used Troopy (1995 1HZJ75). Ive discovered that the windscreen washer doesnt work.

What we have found so far is that the wiper switch was faulty. Which we have replaced. But there is still something wrong.

I know the switch works now, because when I pull the lever the wipers wipe 3 times as if there was water on the screen. Plus, if someone holds the pump while I pull the lever the pump "bumps" as if its trying to work, but doesnt quite get there.

We know the pump works (have tested it idependantly). I know the lines are clear of gunk (have blown them through). When we test the wiring it appears to be fine and so does the plug that the pump sits in (tested wiring and pump using a multimeter).
My only guess is that perhaps the wiring or plug that the pump plugs into has a break that is not letting quite enough power through to power the pump.....
but to be honest Im lost now.

Does anyone have any clues that I can check out? This is my last try before giving the car to an auto electrician to work out (then he can wire up the driving lights while he is at it I guess).

Thanks for any advice