Here is the Diesel Giant Site with the pictorial how to do the Glow Plug check.
http://www.dieselgiant.com/glowplugrepair.htm
I think on my Multi Meter the Lowest setting is 200 ohms.
For your lock/ignition problems
Ignition Cylinder Tumbler replacement; mixed diesel/gas
I do not know if WD40 can freeze up at -10; the alternative is powerded Graphite that comes in a little squeeze tube;but if you squirts some in the Key Hole and it becomes easier to use it could mean your Ignition Key Tumbler is on the way out.
If it turns out the Ignition Switch itself is bad. I can access mine after the Kick panel is removed looking up from below. 2 screws hold it in place.