Glow plug light sometimes works and sometimes dont

[Swisstonihasher]

Hey all, 1.4 02 TDCI

Have an issue with glow plug light, going do more testing to see if circuit is live when first turn the ignition (being this cold outside it should!). Last few days its been working until yesterday when again no glow plug light and 2 - 3 times to start and idle little lumpy (not loads mind).

I changed the glow plugs for new Ford items (not easy task without rocker off), and brand new hefty battery, seemed better for about 2-3 weeks, back to square one again.

The ecu controls glow plug action via sensor, air inlet temp sensor, any idea where that is? After initial start it then monitors fuel temp and other items for more juice to plugs or not according to Haines, is that right?