fuel breather problem seems to have gone. tank isn't trying to suck itself inside out now.

as for the tail lights and plate lights - i will be getting the multimeter out tomorrow - they all share the same earth according to my haynes manual.

I had a pull from Plod on the way back from the nurburgring, just off the ferry, no rear lights!! Brakes lights were fine, just no rears or numberplates. I Changed the bulbs and all was well and has been for the past 18 months!

As for the misfire, sounds like two unconnected problems