My wife has a 2006 C Max. 1.6TDi 5-speed. She had another irate driver tell her that her reverse lamps weren't working.
After narrowing down the bulbs (both OK) and the fuse in the main fuse box (also OK), I Googled for some answers. There are a few posts on the forums here with explanations on the reverse light switch. I couldn't find any with clear pictures though so hopefully this will help someone else.
If the bulbs and fuse are OK and your reversing lights don't work, then the chances are that the problem is the switch. The switch is located on the gearbox. In my case, on top of the gearbox. It is a relatively simple fix though.
Tools required:
Flat head screwdriver
22mm spanner (or set of vice grips)
patience
Parts needed:
Part number CM5Z-15520-B. In this case, £16 from a main Ford dealer:
The location of the switch is underneath the battery - at the top right of the engine bay in this photo. However, you don't need to remove the battery. Removing the air filter box (circled) will give you enough access.
There is a small, thick rubber band to pop off - visible at the bottom of the picture below.
You also need to disconnect the sensor cable and then the large hose from the air filter box.
Once you have removed the band, the hose and the sensor cable, you can lift the air filter box out. You may need to jiggle it slightly. There is nothing else securing the box but it is set into guide holes.
The picture below shows what it should look like with the air box gone. It took me a while to search around and find the reverse switch, so I have circled the area to look for.
If in doubt, look for cable that goes to the switch. There is a hose containing cables, the reverse light switch branches off the other cables as below. Battery is marked for reference:
Once you find the switch, pop the cable off the top of it. Again, if in doubt, this is right below the battery but you should be able to reach through and see the switch sticking up:
Take your spanner (or vice grips) and remove the switch. This took a bit of effort but once it unstuck, I could unscrew it by hand fairly easily.
Old switch alongside the shiny new switch:
Take the new switch, screw it in by hand, taking care to make sure it is in straight. Give it a tighten with the spanner and then pop the cable back on. The cable can only fit on one way.
You can then pop the air filter box back in, connect the sensor cable and hose again. You should be good to go.
Total time was probably about 40 minutes. But that was me taking my time and also searching around a bit for where the switch was located.