Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Circuit Functions
The circuit designation system for wiring has been designed to provide complete vehicle logic to the method of naming circuits. This system has been formulated from a whole vehicle point of view.
All circuits in the wiring diagrams use an alpha/numeric code to identify the wire and its function. To identify which circuit code applies to a system, refer to the Circuit Identification Code Chart below.
This chart shows the main circuits only and does not show the secondary codes that may apply to some models.
| CIRCUIT CODE | FUNCTION |
|---|---|
| A | BATTERY FEED CIRCUITS (PRIMARY DEDICATED MULTI-SYSTEM FEEDS) (i.e. FUSE LINK FEEDS, FUSE PROTECTION DEVICES, STARTER FEED STARTER RELAY FEED) |
| B | BRAKE CIRCUITS |
| C | CLIMATE CONTROL CIRCUITS (i.e. A/C, HEATER, EBL, HEATED MIRROR) |
| D | DIAGNOSTIC COMMUNICATION CIRCUITS (i.e. Ethernet, CAN, LIN, PCI) |
| E | DIMMING ILLUMINATION CIRCUITS |
| F | FUSED CIRCUITS (SECONDARY FEED FROM PRIMARY FEEDS) |
| G | MONITORING CIRCUITS (i.e. GAGES, CLOCK, WARNING DEVICES) |
| H | **OPEN** |
| I | NOT USED AS A CIRCUIT DESIGNATION |
| J | **OPEN** |
| K | ENGINE LOGIC MODULE CONTROL CIRCUITS |
| L | EXTERIOR LIGHTING CIRCUITS |
| M | INTERIOR LIGHTING CIRCUITS (i.e. DOME/COURTESY/CARGO) |
| N | ESA MODULE ELECTRONIC CIRCUITS |
| O | NOT USED AS A CIRCUIT DESIGNATION |
| P | POWER OPTION CIRCUITS (BATT. FEED) (i.e. SEAT, DOOR LOCKS, MIRROR) |
| Q | POWER OPTION CIRCUITS (IGNITION FEED) (i.e. WINDOWS, SUNROOF) |
| R | PASSIVE RESTRAINT CIRCUITS |
| S | SUSPENSION AND STEERING CIRCUITS |
| T | TRANSMISSION, TRANSAXLE, DIFFERENTIAL, AND TRANSFER CASE CIRCUITS |
| U | **OPEN** |
| V | SPEED CONTROL, AND WIPER/WASHER CIRCUITS |
| W | **OPEN** |
| X | SOUND SYSTEMS (i.e. RADIO, HORN) |
| Y | **OPEN** |
| Z | GROUNDS (NON DEDICATED MULTI-SYSTEM GROUNDS) |
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.