Having purchased the switch recommended by Dezufo, i was assuming (quite wrongly) that the change from old to new would be straightforward. The current switch has four wires. Two red - one feed in; the other out to the single after market fog lamp - and two black. One black I assume is to earth the in switch warning light, but what would the other black be for? The new switch also has four wires, black for earth, red as feed in, green to lamp and a yellow marked as positive. What is the pupose of the yellow wire and what should it connect to? I thought I understood car electrics, but this has me really stumped!