Bad Harness causing gas tank problems???

[knicksplayer]

Hi everyone,

I brought my 02 Porsche boxster to the dealer because I got a P0455 CEL Large Leak (Evap) check engine code. The front part of my harness (near the right side
turn" indicator) is in bad shape and the mechanic claimed that may be the problem. I felt he wasn't confident in what he was saying and given that the harness change costs like $4,000 (that's what he quoted!!!), I feel he's trying to play me. The bad harness causes my abs and psm lights to be on and after testing the car in extreme situations, it doesn't cause a safety issue. Anyways, back the EVAP problem, my gas tank spits back fuel and I think it would imply that it's simply a bad EVAP and that the engine check indicator therefore makes sense?? Does anyone know what exactly would have to be done if that was the case? I changed the fuse, the problem isn't that simple (I wish) and I don't hear that clicking sound when I push the metal flap out of the way. But what I do hear is some kind of air coming out of the tank when the metal flap is slightly open? That would explain the problem by law of physics, the air/vapor would be the cause of the fuel spit...

So that's about it, that's the story, any comments will be appreciated. Thanks!