As Sundance says it will almost certainly be an earth, download & study the diagram, don't be put off with the complexity, for the most part what you have is several simple circuits all knitted together: a multiple of battery & bulb circuits. My guess would be, dependant on model, earth headers 0550 (k108) or 0553 (k108) for the f & K109 for the tf. There is another electrical supplement which shows where the various connections are. Rummage around a bit & I'm sure you'll sort it. Don't get bogged down with “electrickery” you wouldn't shit yourself if you had a torch to mend, you've just got several “torches”. Mike.