I've had my share of backfeed weirdness from changing them out. Right now I just discovered that my front marker lights are coming on when I hit the brakes, and the left turn signal stops flashing also when I hit the brakes. I did the ones in the cluster, and all the backlights were fine but when I did the warning lamps they were on at a low glow when the headlights and markers were on. Had to go back to incandescents for all the warning indicators but kept the CHECK GAGES, turn signals, low fuel warning and HI beams as LED. I'll still have to undo some more, because something in the brake circuit is backfeeding. I would check everything in the dark, preferably with a helper while you hit the brakes, before you put it all back together and call it good. I also found out the hard way that replacing the CHMSL bulbs will freak out the ABS computer.