Unfortunately, it's the harness. There's a problem with the gears (automatic). The transmission is fine - the electrics person found the problem, which is two wires that have fused together. He's going to have a go at replacing them, but apparently the wiring harness is a bit temperamental and not that conducive to fiddling around with, so he said that if his fix-it-up didn't work, he'd have no option but to replace the whole unit.