do it during the day maybe?

its a known fact that my00 and earlier wrx's had terrible earths.

my lights used to dimm when i wound windows up or down.

i fixed it by running a couple more earths, from the negative terminal to more body panels.

Yep... fix your earth, and if you really want get a Optima YellowTop for the overkill :D if your lights dim with one of them babies you're doing something wrong :p

rich x: i have got a sub and amp but they only dim when i pull up the hand brake.
baurepaires: get higher wattage globes but that would require pulling the dash appart.
fobz: yes allways on full but thats the speedo and rpm gauge not head lights control.
darkmoose: the lights are all the same just with different colored condoms/covers.
the only thing i can think of is if the lhandbrake light is in series with the headlights but its more than likely that its bad earth. might run a new 16mm ground wire to the body.

sounds like soft suspension to me.