Automotive Wiring Color Codes & Terminal Designations
Standardizing wire colors and terminal numbering is critical for diagnostics and repair. While OEMs have proprietary systems, the aftermarket heavily relies on the DIN 72552 standard for terminal designations.
DIN 72552 Terminal Standard
This German standard dictates the numerical codes found on automotive relays, ignition switches, and alternators. Memorizing the core numbers is essential for any wiring professional.
| Terminal | Definition | Common Application |
|---|---|---|
| 30 | Battery Positive (Constant) | Direct from battery, unfused or main fuse. Always hot. |
| 15 | Switched Positive (Ignition) | Hot in RUN and START. Powers engine management. |
| 31 | Battery Negative (Ground) | Chassis ground return path. |
| 85 | Relay Coil (-) | Trigger ground for standard Bosch-style relays. |
| 86 | Relay Coil (+) | Trigger power for standard Bosch-style relays. |
| 87 | Relay Normally Open (NO) | Output to load when relay is energized. |
| 87a | Relay Normally Closed (NC) | Output to load when relay is at rest. |
| 50 | Starter Control | Hot only in START position. |
Common Aftermarket Color Codes
While OEMs vary wildly (Ford's system is vastly different from GM's), the aftermarket generally adheres to a standardized color logic for universal harnesses and accessories.
- Red: Constant 12V+ (Terminal 30)
- Black: Ground / Chassis Return (Terminal 31)
- Yellow: Switched 12V+ Ignition (Terminal 15)
- Blue: Antenna Turn-on / Accessory trigger
- Green: Often used for fuel pump feeds or specific sensor signals.
Note: Always use striped wire (e.g., White with a Black stripe, denoted as WHT/BLK) when running multiple signal wires in the same bundle to prevent cross-pinning during termination.