The electrical components will do what it can to find a ground. Even feed back through other items. You ever see the car that turns on its blinker on to see the lights alternate from left to right, but 1 is brighter? Usually thats a bad ground in the socket and its using the ground from the other side. Did you do a voltage drop from the battery to the ground? Put the lead on the positive and then move from the battery post to the cable, to the other end of the ground cable to the bolt to the frame. All the while leave the red lead on the positive. Also, try removing fuses of hte affected circuits and see if the problem persists. This may help narrow down the circuit.