Having read through more than my share of auto electrical threads trying to sort the Mogster's wipers (with eventual success) I'll try and keep it simple.
Have done a rebody with a Suzuki Vitara chassis and complete running gear, and switches.
Wired up new headlights to existing wiring, every thing was fine.
Tried the lights one day and one of the headlights just glowed, didn't shine, eventually it stopped working and then I found a blown 3 amp fuse in the fusebox instead of a 15A that the other side has.
New fuse in, everything fine then today, at the MOT, it had blown the 15A.
New fuse, all is well, for now, and may stay that way, or it might pop it again.
MOT guy reckons bad earth, get the multimeter out and the earth to the bulb 'beeps' fine to the chassis, BUT, it also reads 12 volts, the same as the other 2 wires to the bulb, but it all works.
Tried earthing together the sidelight and headlight but this results in the sidelights being on permanently regardless of the switch position.
Also have noticed the feed to the headlights seems to be live permanently, even when I click the killswitch that I put in to the fusebox in the cabin.
I'm hoping someone who knows more about these things than me (not difficult!) can offer an answer involving switched earth or something rather than 'it sounds like a hell of a mess rip it all out and start over'.
Many thanks folks.