The direct answer to reading a wiring diagram for a DPDT switch (Double Pole Double Throw) lies in understanding its 6-pin physical layout: the two center pins are the common poles (power input or output), and the four outer pins are the throws (load connections). To wire a standard DPDT toggle for DC motor polarity reversal, you feed power into the center pins, cross-wire the outer pins in an 'X' pattern, and route the resulting outputs to the motor terminals. The ground return path bypasses the switch entirely.

Unlike a simple SPST (Single Pole Single Throw) on/off switch, a DPDT switch manages two completely isolated circuits simultaneously, or manipulates a single circuit to reverse current flow. Below is a complete, table-forward walkthrough of the schematic symbols, physical terminal mappings, and a precise node-by-node trace for the most common DIY application: DC motor reversing.

Decoding the DPDT Schematic Symbol and Physical Terminals

Before tracing the wires, you must map the schematic symbol to the physical metal lugs on the back of the switch. In standard electrical schematics, the DPDT symbol is drawn as two separate SPDT (Single Pole Double Throw) switches linked by a dashed mechanical line. This dashed line indicates that a single physical actuator (the toggle bat or rocker) moves both internal contacts simultaneously.

On a physical 6-pin toggle switch (such as the common CK Components 7200 series or Carling V-Series), the pins are typically arranged in two columns of three. The center pins are your 'Commons' (the poles), and the outer pins are your 'Throws'. If you wire power to the throws instead of the commons, you risk creating a dead short when the toggle is actuated.

Bench Tip: Always identify the commons first. On standard bat-handle toggles, the commons are the middle pins in each column. On some European-spec rockers, the pin numbering may be printed on the plastic housing (e.g., pins 2 and 5 are commons). Never assume pinout based solely on physical spacing; verify with a multimeter.

Here is the definitive terminal mapping and continuity state for a standard maintained ON-ON DPDT switch:

Pin Number Physical Location Function Continuity (Toggle UP) Continuity (Toggle DOWN)
1 Left Column, Top Throw (Normally Closed) Closed to Pin 2 Open
2 Left Column, Center Common (Pole 1) Closed to Pin 1 Closed to Pin 3
3 Left Column, Bottom Throw (Normally Open) Open Closed to Pin 2
4 Right Column, Top Throw (Normally Closed) Closed to Pin 5 Open
5 Right Column, Center Common (Pole 2) Closed to Pin 4 Closed to Pin 6
6 Right Column, Bottom Throw (Normally Open) Open Closed to Pin 5

Node-by-Node Wiring Trace: DC Motor Reversing Circuit

The most frequent use case for a DPDT switch in robotics, automotive winches, and DIY workbench tools is reversing the polarity of a DC motor. Because DC motors change rotational direction when the voltage polarity across their terminals is swapped, the DPDT switch acts as an H-bridge, mechanically routing the positive and negative feeds to opposite motor terminals depending on the toggle position.

Below is the exact node-by-node trace for a 12V DC motor reversing circuit. This trace assumes a standard maintained ON-ON DPDT toggle switch.

1. The Power Source and Input Path

  • Node A (Source Positive): 12V DC positive terminal connects to a 15A inline fuse, then routes to Pin 2 (Left Common) and Pin 5 (Right Common). Jumper a wire directly between Pin 2 and Pin 5 to feed both poles from a single positive source.
  • Node B (Source Negative / Ground Path): The 12V DC negative terminal (ground) bypasses the switch entirely. It routes directly to the motor's chassis ground or the negative return wire. Never switch the ground return on a simple reversing circuit; it complicates the wiring and offers no safety benefit over switching the hot leads.

2. The Cross-Wiring 'X' Pattern (The Throws)

This is where the polarity swap happens. You must install two jumper wires across the outer throw pins to create an 'X' pattern on the back of the switch.

  • Jumper 1: Connect Pin 1 (Left Top) to Pin 6 (Right Bottom).
  • Jumper 2: Connect Pin 3 (Left Bottom) to Pin 4 (Right Top).

3. The Load Output Path

  • Motor Terminal A: Connects to the junction of Pin 1 and Pin 6.
  • Motor Terminal B: Connects to the junction of Pin 3 and Pin 4.

4. Actuation Trace (How the Current Flows)

When you flip the toggle UP, Pin 2 connects to Pin 1, and Pin 5 connects to Pin 4. Current flows from the source into Pin 2, out of Pin 1 to Motor Terminal A (Positive). The return path flows from Motor Terminal B into Pin 3, crosses Jumper 2 to Pin 4, and into Pin 5, completing the circuit back to the source. The motor spins forward.

When you flip the toggle DOWN, Pin 2 connects to Pin 3, and Pin 5 connects to Pin 6. Current flows into Pin 2, out of Pin 3 to Motor Terminal B (Positive). The return flows from Motor Terminal A into Pin 1, crosses Jumper 1 to Pin 6, and into Pin 5. The polarity at the motor is now reversed, and the motor spins in reverse. For deeper theory on mechanical switching topologies, All About Circuits provides an excellent breakdown of pole and throw mechanics.

Step-by-Step Verification with a Multimeter

Never apply power to a newly wired DPDT switch without verifying the internal contacts and your jumper placement. A misplaced jumper on the throws will result in a direct short across your power supply the moment you flip the toggle, potentially melting wires or destroying your power source.

  1. Set the Meter: Turn your multimeter dial to the Continuity setting (the symbol resembling a sound wave or Wi-Fi icon). Touch the red and black probes together to verify the meter beeps and reads near 0.0 ohms.
  2. Verify the Commons: With the switch disconnected from all power and loads, place the black probe on Pin 2. Place the red probe on Pin 1. Flip the toggle UP. The meter should beep. Flip the toggle DOWN. The beep should stop, and moving the red probe to Pin 3 should trigger a beep. This confirms your left pole is functioning correctly.
  3. Verify the Right Pole: Move the black probe to Pin 5. Test continuity to Pin 4 (UP) and Pin 6 (DOWN). Both should behave identically to the left pole.
  4. Verify the 'X' Jumpers: Place one probe on Pin 1 and the other on Pin 6. The meter must beep continuously, regardless of the toggle position, confirming Jumper 1 is solid. Repeat for Pin 3 and Pin 4 to verify Jumper 2.
  5. Check for Shorts: Place probes on Pin 1 and Pin 3. The meter should read 'OL' (Open Loop) or infinite resistance in both toggle positions. If it beeps, your jumper wires are touching, or the switch internals are shorted.
Safety Warning: If you are using an ON-OFF-ON (center-off) DPDT switch for motor reversing, be aware that the center position breaks the circuit, but rapid toggling through the center can cause inductive voltage spikes (back-EMF) from the motor. Always install a flyback diode (e.g., 1N5408) across the motor terminals to protect the switch contacts from arcing and pitting.

Common DPDT Wiring Configurations Compared

While motor reversing is the most popular application, the wiring diagram for a DPDT switch can be adapted for several other bench and field tasks. The physical switch remains the same, but the jumper placement and load routing change drastically. Electronics Tutorials outlines various switching configurations that leverage this versatile component.

Configuration Jumper Requirement Power Input Location Primary Use Case
DC Motor Reversing Two cross-jumpers (1-to-6, 3-to-4) Center Commons (Pins 2 & 5) Winches, conveyor belts, robotics
Dual Independent Circuits None Center Commons (Pins 2 & 5) Switching two separate 12V lights or pumps simultaneously
Input Selector (A/B Switch) One straight jumper (1-to-4) Outer Throws (Pins 1, 3, 4, 6) Audio routing, selecting between two sensors to one ADC
Series/Parallel Battery Complex multi-wire bridging Varies by battery topology Switching 2x 12V batteries between 12V parallel and 24V series

When building an Input Selector (A/B Switch), the logic flips: the loads connect to the center commons (Pins 2 and 5, which are jumpered together to feed a single input like an amplifier), and the two separate sources connect to the outer throws. This prevents the two sources from ever back-feeding into each other, a critical safety requirement when switching between two separate DC power supplies or audio signals.

Understanding the exact pinout and tracing the current path node-by-node ensures your DPDT switch performs exactly as intended, whether you are reversing a high-torque wiper motor on a workbench or routing sensitive analog signals in a custom enclosure. Always verify with a meter, respect the ground path, and use the correct ampacity wire for your specific load.