top brake light affected by main light switch

[aswjetta]

Just curious if anyone has any idea why my top (third) brake light turns on all the time when I turn the main light switch on. When the switch is on my tail lights turn on and the top brake light won't shut off even when the brake isn't pressed so that there is no difference when the brake if pressed. I've checked the fuses and none appear blown. Anyone have an ideas?

Thanks