If you have your owner's manual, read it carefully. When the glow light on the dash doesn't come on, that *usually* means one or more glow plugs is out. You can then test them with a meter to determine which one is bad, or just replace them all and keep the old good ones as spares. Use Bosch or Beru plugs, not Autolite or Monark. Check the flat 80A fuse in the glow plug relay first, though.
When changing the plugs, it wouldn't hurt to crank the engine over to blow out carbon bits. This shouldn't be necessary if the engine is driven hard regularly and the plugs come out easily. I'm lost about the door panels - all this work is in the engine compartment...
