04 Nuevo high level brake light.

Learning lots form this forum, cheers. I need to replace the high level brake light on my van as it's full of water and packed up. I've managed to slightly pry it from the recess, as it appears to be fastened by sticky pads, but there is no slack whatsoever in the cable. My question is do I have to remove the rear cabinets to get at the cable and hopefully get a bit of slack. Also can anyone tell me where I can source a new light.
Al.

As my van's MoT is due I finally got round to doing this job this weekend. I don't know if the high brake light is a requirement for the MoT, but it was flagged up last year and I figured if it was flagged again it might mean a fail. I obtained the light from Autosleepers very efficient, if expensive, parts department for around £40.
With lots of careful prising and levering the old light came away slightly, it was suck fast at the back with silicone. This gave me just enough room to chip away with a small craft knife at the silicone that filled the hole in the van body round the wires. After half an hour they were free enough to ease out and get access to the spade connections.
It's essential you do this bit carefully as any tugging will lead to the spade terminals coming apart and the feed wires dropping back inside the body cavity never to be seen again!
New lamp connected up with gaffer tape to help hold the terminals together for next time and fixed back into the recess with silicone. Just as an extra precaution against water ingress I ran a bead of silicone along the top and sides of the fitted light. Job done.