wiring the extruder

[keos]

on the extruder which cable is negative and which cable is positive; the QU-BD extruders have two cables and both are white.....

Thankx
Keos

[orcinus]

It doesn't matter.
It's a resistor. And there is no contact with the mass (shield/gnd).
And even if there was, there is no connection between the gnd on the LV side of your power supply and the earth on the HV side of your power supply.

In short - it doesn't matter.