Cosa Electrical Problem

Ok I have an electrical probem with my Cosa.

When you turn the key the Neutral light comes on but very gently flickers. If you use anything that draws power (fuel tap, horn, parking lights) then the neutral light pretty much goes out. I guess this means there is a short somewhere, does anyone have any idea if this will be with a component (rectifier, relay etc) or more likely in an untraceable wire?!?! Any ideas???

Also if you run it is revs up to around 4 to 5k but won't rev on past this.