What can anyone do to add more circuits in a car without adding more switches? The answer is the DPDT toggle switch. Those letters stand for "double pole/double throw," and this type of switch can solve the problem of having to mount an excessive number of toggle switches in a dashboard.
Determine which circuits will be controlled by the DPDT switch. One switch can take the place of four simple SPST (single pole/single throw) toggle switches.
Connect the centre terminals of the switch to a fused power source using solderless terminals and automotive primary wire. You will need to connect each terminal to a power source. This feature allows the use of two differently fused circuits.
Connect the terminals on each end of the switch to the circuits the switch will be controlling. Be aware that flipping the switch in one direction will turn on both circuits connected to one end of the switch, and flipping the toggle in the other direction will shut those two devices off and turn on the circuits connected to the opposite end of the switch. Switches are also available with no off position in the centre. Using this type will make controlling circuits an either/or type of control.