USB Cable Wiring Diagram: USB-A, USB-C, and Micro-USB Pinouts

USB (Universal Serial Bus) cables look simple from the outside, but the pinout -- which conductor goes where -- matters the moment you need to repair a cable, build a custom harness, or troubleshoot a charging or data problem. This guide covers the pin assignments for USB-A, USB-C, and Micro-USB connectors, the standard wire color codes, the difference between power-only and data cables, and USB OTG wiring.

USB-A (Standard Type-A) Pinout

USB-A is the rectangular plug that most people still think of as "the USB connector" -- the type that plugs into computers, chargers, and hubs. It has four pins.

USB-A Pin Assignment

Pin 1 is on the right side when the plug is oriented with the flat (Trident logo) side up and the opening facing you.

Memory aid: Red, White, Green, Black -- outside-in from the pin 1 side, or think of it as matching the US/Mexico flag colors from left to right.

USB-A Current Ratings

• USB 1.1 / USB 2.0: 500 mA (unit load)
• USB 3.0: 900 mA (unit load)
• USB Battery Charging 1.2 (BC1.2): Up to 1.5A
• USB Power Delivery (via USB-C adapter): Up to 240W

A standard USB-A charger that reports itself as a "dedicated charging port" (DCP) shorts D+ and D− together (or uses Apple proprietary voltages on D+/D−) to signal the device that higher current is available. This is why a phone charges faster from a proper wall adapter than from a PC USB port.

Micro-USB Pinout

Micro-USB was the dominant smartphone and tablet connector from roughly 2007 to 2019. It has five pins in a smaller rectangular shell.

Micro-USB (Micro-B) Pin Assignment

The same four signal conductors as USB-A (VBUS, D−, D+, GND) occupy pins 1 through 3 and 5. Pin 4 is the ID pin, which is used for USB OTG (On-The-Go) detection -- see the OTG section below.

When making a standard Micro-USB cable (Type-A to Micro-B):

• USB-A pin 1 (Red/VBUS) connects to Micro-B pin 1
• USB-A pin 2 (White/D−) connects to Micro-B pin 2
• USB-A pin 3 (Green/D+) connects to Micro-B pin 3
• USB-A pin 4 (GND) connects to Micro-B pin 5
• Micro-B pin 4 (ID) is left unconnected in a standard host cable

USB-C Pinout

USB-C is a 24-pin connector with a symmetrical, reversible design. The full pinout is complex, but for practical wiring purposes the important groups are:

USB-C 24-Pin Layout

The 24 pins are arranged in two rows (12 pins per side, A1-A12 and B1-B12), which allows plug insertion in either orientation.

CC Pins (Configuration Channel)

The CC pins are what make USB-C "smart." They serve several functions:

• Cable orientation detection: When a USB-C cable is plugged in either way, the CC pins tell the host which orientation was used, allowing the correct data lines to be enabled.
• Current advertisement: The host (charger) places a pull-up resistor on CC to signal how much current it can supply (default 900 mA, 1.5A, or 3A).
• USB Power Delivery negotiation: USB PD uses CC pins to negotiate voltages and power levels (5V, 9V, 15V, 20V, and power levels up to 240W in USB PD 3.1).

A passive USB-C cable (for charging and USB 2.0 data only) needs only VBUS, GND, D+, D−, and the CC pins. A cable rated for USB 3.2 or Thunderbolt 3/4 includes the SuperSpeed differential pairs and active electronics in the cable plug assembly.

USB-C Wire Colors in Practice

The USB-IF does not mandate specific wire colors for internal cable construction, but common third-party cable conventions include:

• Red or orange: VBUS
• Black: GND
• White and green (or data pair colors): D+ and D−
• Blue / yellow: SuperSpeed pairs

If you are cutting open a USB-C cable, use a multimeter to trace continuity rather than relying on wire colors.

Power vs Data Cables

Not all USB cables carry data. Many cheap charging cables include only VBUS and GND, omitting the D+ and D− data lines. These cables charge any device but cannot be used for file transfer, syncing, or firmware updates.

To check: plug the cable into a phone and a computer. If the computer does not detect the phone at all (no "Trust this computer?" prompt on iPhone, no device in Device Manager), the cable is charge-only.

For a proper USB 2.0 cable: 4 conductors (VBUS, D−, D+, GND). For USB 3.2 Gen 1 (formerly USB 3.0): 9 conductors -- the 4 USB 2.0 wires plus two differential pairs for SuperSpeed (SS) TX and RX, each with a separate ground. For USB 3.2 Gen 2x2 and Thunderbolt 3/4: even more complex, with full 40-pair layouts and active retimers in the cable assembly.

USB OTG (On-The-Go) Wiring

USB OTG allows a device that is normally a peripheral (like a phone) to act as a USB host and control other peripherals (USB drives, keyboards, MIDI controllers).

Micro-USB OTG Cable

A Micro-USB OTG adapter is a short cable with a Micro-B plug on one end (for the phone) and a USB-A socket on the other (for the peripheral).

The only electrical difference from a standard Micro-USB cable is pin 4 (ID) is connected to GND (pin 5) at the Micro-B end. The phone detects the short between ID and GND and switches from peripheral to host mode.

USB-C OTG

On USB-C, OTG mode is determined by the CC pin configuration and the device's capability negotiation -- no physical short is needed. Devices that support USB-C OTG advertise dual-role port (DRP) capability via the CC pins.

Common USB Wiring Problems

• Charging but no data: D+ and D− wires missing, broken, or not connected. Common in cheap charge-only cables.
• Intermittent connection: Damaged VBUS or GND wire near the strain relief (most common failure point).
• Fast charging not working: Charging protocol signals (D+ / D− voltage levels for Apple or Qualcomm Quick Charge) are not present. The cable may work but the charger's BC1.2 or proprietary detection signals are not reaching the device.
• OTG not detected: ID pin not shorted to GND in a Micro-USB OTG cable, or the device does not support OTG.

Create Your Own USB Wiring Diagram

Planning a USB charging station, custom cable harness, or embedded USB interface is much cleaner with a proper diagram. With CircuitDiagramMaker, you can:

• Draw USB-A, Micro-USB, and USB-C connector pinouts with labeled pin numbers and wire colors
• Show cable wiring for standard, charge-only, OTG, and USB PD applications
• Diagram USB hubs with power distribution and upstream/downstream ports
• Add notes on current ratings, PD contracts, and protocol compatibility
• Export the diagram for hardware documentation or team reference

Create your own USB cable wiring diagram -- free

Key Takeaways

• USB-A has four pins: VBUS (red), D− (white), D+ (green), GND (black) -- in that order from pin 1 to pin 4.
• Micro-USB adds a fifth ID pin used for OTG detection -- shorting ID to GND at the device plug switches the port to host mode.
• USB-C uses 24 pins in a reversible symmetrical layout. CC pins handle orientation detection, current advertisement, and USB Power Delivery negotiation.
• Charge-only cables omit D+ and D− -- they charge devices but cannot transfer data.
• USB PD (Power Delivery) operates over the CC pins and can negotiate voltages up to 48V and power levels up to 240W (USB PD 3.1).
• Internal cable wire colors are not standardized by USB-IF for all cable types -- use a multimeter to verify pin-to-conductor mapping.
• The most common cable failure point is near the strain relief at either end -- the conductors fatigue with repeated bending.