No Heater Plug Light?

Howdie-Ho everybody! Am new to the forum (and running a Landrover) and have a couple of problems i cant seem to get my hairy head around. If anyone could help i'd be most chuffed..
Its a bog standard 96 300tdi Disco btw-
1/ Since i bought it, it's never had a glow plug/preheat light on the dash even when cold. Have swapped the binacle to see if the light was buggered but still nuffin. Can it be knack'd glow plugs? It always starts 1st time even from cold. Being a such a tight bastard, i've always run diesels and they've never started without heat or a few minutes turning over!

2/ Actually, sometimes it doesn't start first time- other times all i get when i turn the key is a click from a green box in the pass side and another click from a yellow relay in the drivers footwell but engine wont turn over. having read some of the posts on here i thought it might be an immobilizer / spider thing so i had the dash out only to find there wasn't a spider..cant see any evidence of one either.
Incidentally- sometimes after i've messed with the relay a bit- given it a tap and a wriggle, it will go though i've changed the relay for one from one of my breakers which never had this problem
Any ideas, Chaps & Chapettes?

sounds like a bad earth to me

Is that for the heater plugs or the 2nd problem? Could well be- had the interior out to do the floors and sills so had to move a lot of the wiring but have been round where they earth to the body and all looks ok.. Must admit i'm a bit of a 'tard when it comes to lectrics! What does the yellow relay actually do?