How To: Fit aftermarket Reverse Sensors

[mart]

I took the rear light cluster off yesterday to check the reverse light wire colour. When I put it back on I had a message on the dash saying Check left position light.
I must of knocked the rear left hand side light bulb or something as when I took it back off and messed with the bulb it disappeared again. However this morning the message is back again, must be a loose connection of something, any ideas ?

While I had the rear lights off I checked to see if I would get a message with the reverse light bulb taken out, but there wasn't. Seems strange that the rear lights are on the can-bus but the reverse light isn't.....