Wiper parts / wiring

I'm having problems getting my 2 speed wiper to work on 2 speeds.
The motor reads 12v 14w park. The plug has 4 wires - Black = Earth Green = +Ve Green/red = speed 1 Green / (what ever the other colour is) = i assume speed 2
Using a on-off-on switch I get speed 1. Speed 2 blow the fuse. If it is unplugged. The fuse doesn't blow. So I assume it is the white nylon pack on the side. Does this have a part number?
Or I could use the resistor pack in the square smiths heater to give me 2 speeds - in which case does any body have a part number for this? Or another solution?

I got a couple of spare wipers, one of the other nylon blocks also blows fuses, the other only works on one speed?

I'm not too worried about park, although it would be nice.

I'm going to get another donor wiper to try. But if anybody canfind a part number for the nylon block on the motor it would be appreciated.