No electrical skillse needed.
If for instance you had no voltmeter you could simply record the position of the various wires (a photo is nice) and remove the Glow Plugs. Usually you will see the loop/filiment/heater element is burned in two.

I believe a 13/16 wernch is the size for your Glow Plugs.

__________________
84 300D, 82 Volvo 244Gl Diesel