The lights are operated by a pressure switch mounted on the fire-wall, it kinda looks like a splitter (well it is) but it has a couple of wires coming out of it. When you apply pressure it is meant to activate the lights.

So I suppose two things can be wrong, mechanical fault (poor pressure) and electrical fault (switch/wiring).

Sounds like all it needs a little clean-up and a few bits and bobs replaced.