Well, following the problems last time with the two lights I installed being WELL below power I went out and purchased a new unit.
The new unit came from Halfords and is basically a fog light unit designed to be bolted to the underside of a cars bumper, so adding a fog light. Its an enclosed square unit including a single 12V bulb and reflector, plus a screwed down red lens.
My idea was to stick with the concept of installing a new, purpose fog light within the passenger side rear light unit. The open "centre" running light lens was a perfect position. It wouldn't detract from the brake light function, and would only enhance the running lights.
The purchased fog light unit was simple to open up. The red lens wouldn't be needed, but the reflector was needed to get the most out of the bulb. However, it was a little on the large size. Kept original it would get in the way of the running light bulb. So, simple fix. Just cut it down to size with a hack saw. This cut-down unit was then wired up with a couple of wires terminating in spade connectors and fixed to the inside of the rear unit using some double-sided foam pads (the sticky types). Bingo, one (concealed) fog light.
The wire back to the switch through the left side pontoon was used, as shown in part 1. As many people have done before I cut a hole in one of the dummy switches for a 16 amp illuminated switch, which would show when the light was on (an MOT requirement). I then needed a live feed from the headlight circuit so the fog light would only work when the headlights were on.
To add this function I tapped into the dipped beam headlight relay in the fuse box. The slot on the left-hand side at you look down from above is the one you want. I simply pushed the bare wire into the slot before re-seating the relay. I'll sort a more permanent connection if all works! It also needs an in-line fuse holder and a 10 amp fuse adding, just to make things safe.
With all connections made the last thing to do was to connect an earth from the illuminated switch to the earth (which I had now found and correctly installed) on the cigarette lighter, allowing it to light when in use.
All back together and it worked! One discreet fog light, without modifying the PCB board, or having to have an ugly light of the back of the car.