When working on 12V automotive or industrial electrical projects, visualizing how a switch functions can be the key to wiring it correctly—and safely. While terms like SPST, SPDT, DPST, and DPDT may sound like alphabet soup at first, they each represent a specific type of switch with a unique wiring configuration. To make things clearer, we’ve created a set of clean, easy-to-follow wiring diagrams that illustrate exactly how each switch operates. Whether you’re wiring up lights, motors, or relays, these schematics will help demystify the logic behind the hardware.
SPST (Single Pole Single Throw)
Basic ON/OFF switch
Wiring Diagram
[+12V] ───(SWITCH)──── [LOAD] ─── GND
Terminal Labels:
- Terminal 1 = Input (Power)
- Terminal 2 = Output (To Load)
SPST Switch Use Cases
- Toggle LED lights on/off
- Activate a 12V fan
- Power a USB charger socket
- Kill switch for a small circuit
SPDT (Single Pole Double Throw)
Select between two outputs, or A/B logic
Wiring Diagram
┌─── [LOAD A]
[+12V] ──(SW)───┤
└─── [LOAD B]
Terminal Labels:
- Common (center) = +12V
- Throw A = Output 1
- Throw B = Output 2
SPDT Switch Use Cases
- Toggle between high beam / low beam circuits
- Choose between two power sources
- Toggle relays (e.g., winch in/out controller)
- Audio source switching in a DIY sound system
DPST (Double Pole Single Throw)
Controls 2 independent circuits simultaneously
Wiring Diagram
[+12V A] ───┐ ┌─── [LOAD A]
(SWITCH)
[+12V B] ───┘ └─── [LOAD B]
Terminal Labels:
- 2 Inputs (A & B)
- 2 Outputs (A & B)
DPST Switch Use Cases
- Switch both positive and ground at once
- Control two lights from one toggle
- Simultaneously power a fan + light
- Power two separate relays at the same time
DPDT (Double Pole Double Throw)
Reverses polarity, or switches two outputs at once
Wiring Diagram (Polarity Reversal for Motor)
MOTOR
│
[C1]────┐ ┌────[NO1]
(SWITCH)
[C2]────┘ └────[NO2]
REVERSE POLARITY ON THROW
Terminal Label
| Terminal | Description |
|---|---|
| C1, C2 | Motor leads (common) |
| NO1, NO2 | Normally Open Throw |
| NC1, NC2 | Normally Closed |
Motor polarity changes depending on switch throw position
DPDT Switch Use Cases
- Reverse 12V motor direction (e.g., actuator, power window, hatch open/close)
- Change between two batteries or power sources
- Toggle LED color modes (red/blue for emergency vehicles)
- Polarity reversal for linear actuators (lift, push/pull arms)
12V Electrical Switch Wiring Diagrams
A well-wired switch isn’t just about getting your circuit to work—it’s about making it reliable, safe, and easy to troubleshoot later. These diagrams serve as a quick-reference tool whether you’re in the garage, the lab, or out in the field. Bookmark this post, print the diagrams, or share them with your team—because when you can see the logic, you can wire with confidence.