Third brake light not working

[mrsuffolk]

Hello, I'm new here, '06 LX Hatchback. The fuse had gone on my brake lights. And it looks like previous owner had replaced it too. Once I put a new one in the left-right ones work but not the top-middle one. I put a voltmeter on it and got ~1v without the brake pedal depressed, and no change with it pushed down. I read online that it could be broken insulation on a wire in the harness where the hatch joins the bodywork but I've thoroughly inspected all that wiring (under and around the various bits of tape and rubber) and it's as good as new. Where do I look next? IS this a common issue? Is it likely grounding somewhere? I'm thinking about removing the "spoiler" (in quotes) next to see if there are any obvious clues in there, anyone got any ideas?

[mrsuffolk]

Update: Took the rear spoiler off this weekend, stripped all the tape/insulation from the wires and they're all in perfect condition, no signs of breaks or brittlness anywhere. Now, though, I'm getting 12v on the left pin of the connector even when ignition is off. If I so much as plug in the centre brake light the fuse goes. The left/right brake lights work perfectly otherwise, so I've just been running without the centre light (hey, if it's not "fiitted" it doesn't have to "work" does it?). Like I said, no evidence at all of shorting at the boot end, where do I look now?