It is the switch inside of the car that you can adjust the dash brightness. It is to the left of the steering column above the change holder.

You shouldn't just replace a part, because we make a suggestion. You really should test the part first.

For example, with the key out of the ignition switch, pry out the dimmer switch and unplug it. Get a piece of wire and connect the wire between the red and black wire. Put the key in the ignition and turn the key to the II position. Turn on the headlight. The dash lights should turn on to their brightest setting.

 

Are you sure that someone hasn't previously put a highbeam in the OTHER low beam socket?

 

YES- Sorry I wasn't clear. I should have put that differently....Test the dash dimmer switch. Shouldn't replace something just on a suggestion-that could get very expensive

If you're going to be doing this kind of stuff more. I would suggest getting a simple volt meter, I've seen some that don't cost much. A test light is ok but sometimes the difference between 10 volts and 12 volts can mean all the difference in the world.