I turn the parking lights on when I go through tunnels so the instrument panels light up, but what happens is the display on my head deck dims to the point I can barely see it.

I don't know if it's normal, but if it is I want to see if I can get it to be fully illuminated all the time.

Any ideas??

Did you wire the Illumination wire of the head unit up? If you did then your head unit will dim when you put your headlights on so that it's not so bright at night.

You should be able to adjust the illumination transition on the head unit if it has it.

If you haven't wired the illumination wire up or your head unit does not have that feature, then your battery/alternator might be dying.

phong =P~

Do you have a fairmont, ghia, or lane? if so try pulling that little switch on your headlight switch up well there on.
Not sure on the lower models.

Its a normal feature. You could disconnect the dimming wire in the loom, or you can probably turn it off. What brand of head unit is it?