Made a discovery (pun intended) about the lights on my 300tdi.

A while ago there was I had an issue that my spotlights were coming on with dipped headlights, this caused me to go through all of the wiring and rewire my spots properly with a relay and all that. I thought everything was fixed but last night I had one headlight on, the other off and the spots on on dipped so I took a multimeter to the plug and it was all sorts of weird.

When I plugged the headlights back in I noticed jiggling the plug made the light work or not, then moved the other (working) side's plug and that got brighter too! So there we go, the bulb holders (plugs) had deteriorated. Fitted two new ones today (£3 ish from halfrauds) and my dipped and main beams are now much brighter.

So if you feel like your driving about with a couple of candles strapped to the front have a look at your plugs and consider replacing them.

Mine were a bit of a state with the plastic cover a wee bit melted and that, apparently they get really hot and you can get ceramic bulb holders instead.

yeah, IF your motor is fitted with the "Dim-dip" lights (Thats the lights that are SUPPOSED to be dimmer than Dipped-beam, when the engine is running), then un-plug the ballast & remove the feature. Basically, the problem having the dim-dipped (Pseudo"day-time running lights") lights is, the electrical connector (3-way plug) over-heats over a period of time, causing the problems you describe.

The dim-dip ballast resistor is normally mounted (On my 300tdi) next to the washer-fluid bottle, on the bulk-head.... a finned yellow-ish block, with an electric-connector on one (Maybe both) ends.....simply disconnect & make sure the wire is tied up out of the way...