My friends civic has this problem whenever he turns his headlight on, the gauges inside his car dims and goes off likelossingpower.. he just bought the car and its used... I'm assuming its the fuse but not so sure. What do you guys think?

 

tell him to check his ground wires. it could be a fuse. it all depends on a ton of other stuff.

does he run some system in the car, has he had the alternator tested recently, is his battery good, etc.

start with what's simple and work on to the hardest stuff. bust out that helm's manual!!

 

Not sure if you checked the obvious yet but there is usually a dial for the brightness of the gauge lights... the gauge lights will be lit up with the headlights off but will go dim with them on if the dial is set to low

 

hes not running a system yet.. he just got the car..

 

it could be that he's got a bad connection behind that interior brightness dial. definately check that out too.