The entire Switch panel is held in place by 3 clips, 1 in the upper left, 2 on the right side, pull the upper left one out first and then wiggle the right side out. The swtich is held to the trim plate by a few clips you can unclip with a small screwdriver. All the wires are on a single loom.
Picture 1 - shows the Rear Fog indicator on the Dash to the right of the seatbelt warning light. On my US spec 318ti the wires were in place, but the bulb was missing, not sure how the Z4 is configured but only wanted to dig so far
.
Picture 2 - Normal rear lights [No Brakes]
Picture 3 - Rear Fogs turned on, which simply turns on the outside brake lights on both rear lights.
Picture 4 - shows the European Switch Panel on a Left Hand drive car, looks to be the same as the Right Hand Drive car.
Picture E - [the Money Shot] shows the back of the switch and the 3 retaining clips. There should be 7 wires coming out of the connector as follows:
Purple [Thin Wire]
Black [Thin Wire]
Yellow w/Black Stripe [Thin Wire]
Yellow
Green
Brown w/Black Stripe
Green w/Yellow Stripe, or maybe Yellow w/Green Stripe