I have changed my ignition switch from one with thick wires to a 300Tdi set up. I wired in the glow plug timer using various online sources but I don't know if it works.
I don't get a dash light. Does the 300Tdi ignition switch have a half way between position II and start, glow plug on setting?

No, it has Off, Aux, Ignition on (run) and start. When you get to 'Ignition on' the glowplugs come on for about 8 seconds (with light), light goes out then you hit start. Don't need to leave it the full 8 seconds, most start straight away like a normal petrol engine. Have you tried measuring for a voltage at the glowplugs (during the 8 seconds), could just be an warning light issue.

Now that I know they should be on I will check.
Cheers