If your Car is has an Automatic Transmissions the typical no cranking issues is caused by the Neutral Safety Switch and or the Shifter Bushings.

If it won't crank in Park but will crank in Neutral (or somethimes it will crank after you jiggle the Shifter around) there is a good case for an issue with the Neutral Safety Switch or the Shifter Bushings.

It could also be the Ignition Switch and that could be part of the issue with the Glow Plugs.

If your Glow Plug Relay as a Strip Fuse check that for Cracks or loose hold down Screws.

I had a crack in my Strip Fuse and got intermittent Glow Plug operation; don't remember what the GP Light did.

__________________
84 300D, 82 Volvo 244Gl Diesel