Sneak Circuits

Understanding sneak circuits can help in quickly diagnosing electrical problems that can, at first, seem very complicated.

A sneak circuit can be defined as an unplanned complete circuit. This type of failure is different than a short circuit.

A sneak circuit can occur when more than one component is using the same ground path or power feed. Sneak circuits can happen if a common ground is lost, a fuse is blown, or a wire is grounded between components.

The most visible sneak circuit on the Saturn vehicle is the headlamp circuit. The headlamp circuits are fed by two fuses, the left headlamp fuse and the right headlamp fuse. Note that the left headlamp fuse feeds both the high and low beam bulbs on the left side of the vehicle. Likewise, the right headlamp fuse feeds both the high and low beam bulbs on the right side of the vehicle. On the ground side of the headlamp circuit the important thing to notice is that both the left and right low beams bulbs are switched on and off together. Likewise, both the left and right high beam bulbs are switched on and off together.

If the left or right headlamp fuse blows, evidence of the sneak circuit will be the headlamp bulbs on the side of the blown fuse glowing dim yellow. This is caused by the sneak circuit from the good headlamp fuse, through the bulbs, to ground through the headlamp switch.