Tail lights and rear heater

When you turn the switch off the taillights come on, sometimes it is both and sometimes just one. I have checked all of the fuses and the brake sensor, but it is not the brake lights. The taillights and the blinkers will blink fast sometimes and work normal. I replaced all the bulbs. If anyone could give me some advice I would greatly appreciate it. Oh yeah, I checked for bad grounds as well and I just do not know. I am clueless.