2007 M2 Electrical Body Builder Reference Guide

Electrical Component Overview

The electrical system of the 2007 M2 model is comprised of various interconnected modules. The diagram illustrates the general layout and primary locations of these components:

• Body lighting Interfaces (Module 353): Located on the vehicle body for lighting connections.
• Trailer Interfaces (Module 296, 297): Connections for trailer electrical systems.
• Dash Switches (Module 329): Switches located on the dashboard for various functions.
• Transmission Interfaces (Grey Plug, Module 34C): Connectors for transmission control, potentially frame-located.
• Engine Interface (Black Plug, Module 148, 163, 87L): Connectors for engine control, potentially frame-located.
• Bulk Head Module (BMH) (Module 32A): The central control module for the electrical system.
• Power Distribution (Module 285 PDM): Distributes power to various modules.
• Power Supply (Module 281): Provides primary power to the system.
• Air Management Unit (AMU) (Multiple Modules): Manages air systems.
• Chassis Module (CHM) (Module 335, 32K): Manages chassis-related functions.
• Tail Light Configurations (Module 294): Controls tail light functions.

Electrical Harness Overview

The electrical system utilizes several distinct harnesses to connect components:

• FORWARD CHASSIS HARNESS (Module 288): Connects to the bulkhead module, underhood PDM, headlamps, side marker/turn lamps, and chassis module.
• POWERTRAIN HARNESS (Module 286, 283): Connects to the bulkhead module and underhood PDM.
• ABS/AMU HARNESS (Module 332): Connects to the forward chassis harness, frame ground studs, AMU, and Wabco ABS ECU.
• AFT CHASSIS HARNESS (Module 28A): Connects to the chassis module and tail lamps.
• OVERHEAD CAB HARNESS (Module 287): Connects inline to the main cab harness, marker lamps, and dome lamp.
• FRONTWALL HARNESS (Module 321): Connects to the bulkhead module, underhood PDM, starter mag switch, wiper motor, low coolant sensor, horn, washer pump, and provides a pass-thru to the main cab harness and powertrain harness.
• MAIN CAB HARNESS (Module 320): Connects to the bulkhead connector, diagnostic connector, MBE VCU or CPC, engine compartment, and gauge cluster.

Main Power Distribution Module (PDM)

The PDM is the central hub for distributing battery power to various control modules. It contains mini fuses to protect power feed circuits. Spare fuse slots are often available for additional customer wiring.

The PDM has four main output connectors.

Common Spare Fuse Locations: F6, F10, F11, F14, F21, F23, F25, F26.

The PDM includes diagrams for its fuse specifications, showing fuse location, connection, primary and secondary functions, and fuse ratings. It also details the pin part numbers for harness connections and provides visual representations of the Engine Harness Plug (Green), Forward Chassis Harness Plug (Blue), and the fuse panel layout.

PDM VBAT Fuse Coverage

The following tables detail the power supply fuses and associated outputs for the Bulkhead Module (BHM) and Chassis Module (CHM), powered by VBAT fuses through the PDM.

Bulkhead Module (BHM) Fuse Coverage

Chassis Module (CHM) Fuse Coverage

Bulk Head Module (BHM)

The Bulkhead Module (BHM) is the command module of the M2 electrical system. It controls other modules via the J1939 network. Mounted on the driver side of the front wall, it connects to interior wiring. The BHM has four harness connections on the engine side and three to the cab interior. It manages system parameters, power flow, and circuit protection. The BHM can support up to 5 smart switches and is programmable via service link. Power is supplied by VBAT fuses in the PDM.

Key Bulkhead Module Outputs: Outputs have defined amperage limits; higher loads may require using outputs as signal power with a relay.

• 20A: Cigar Lighter Output (B5.F)
• 12A: Horn (B3.E)
• 12A Combined: SPARE (Utility Light/Spotlight) (B5.E / B4.M)
• 12A Combined: SPARE (Ignition) (B5.G)
• 12A Combined: Panel Lamps (B5.H)
• 6.7A Combined: Panel Lamps (Smart Switch) (B7.A1)
• 6.7A Combined: SPARE (Left Heated Mirror) (B4.F)
• 6.7A Combined: SPARE (Right Heated Mirror) (B4.E)
• 6.7A Combined: Accessory (HVAC) (B6.A9)
• 6.7A Combined: Accessory (Radio) (B6.A10)
• 6.7A Combined: Battery (Dome Lamps) (B5.A)
• 6.7A Combined: Battery (Smart Switch) (B7.A12)
• 6.7A Combined: Ignition (VCU) (B6.A8)
• 6.7A Combined: Ignition (Engine) (B2.K)
• 6.7A Combined: Ignition (ABS) (B1.P)
• 6.7A Combined: Ignition (Trans) (B2.L)
• 6.7A Combined: Fuel Water Sensor Power (B1.F)
• 6.7A Combined: Wake Up (Instrument Cluster) (B5.D)
• 6.7A Combined: Dome Lamps Switched (B5.B)
• 6.7A Combined: Left High Beam (B1.L)
• 6.7A Combined: Left Low Beam (B1.R)
• 6.7A Combined: Clearance Lamps (B5.C)
• 6.7A Combined: Tail/License Plate/Trailer Relay (B1.K)
• 6.7A Combined: Wiper High (B3.F)
• 6.7A Combined: Wiper Low (B3.H)
• 6.7A Combined: Washer Pump (B3.G)
• 6.7A Combined: AC Clutch (B2.M)
• 6.7A Combined: Starter Relay (Crank) (B4.B)

The module has multiple harness connectors: B1 (Forward Chassis), B2 (Engine), B3 & B4 (Front Wall), B5, B6, B7 (Dash).

Detailed pinout tables are provided for each connector (B1-B7).

Chassis Module (CHM)

The Chassis Module (CHM) and Expansion Module (EXM) act as slaves to the BHM, responding to its commands and broadcasting input/output status. A vehicle always has a CHM, but may have an EXM for optional features. Both modules share pin connections.

The CHM is available in two configurations: Standard (rarely used, uses C1, C3, C4 connectors) and Full. It is typically mounted on the LH rail or in an under-cab position.

Key Chassis Module Outputs:

• 20A: Optional Fuel Water Separator Heater (C3-A)
• 10A Combined: Left Park Lamp (C4-C), Right Park Lamp (C4-L), Left Marker Lamp (C4-D), Right Marker Lamp (C4-M)
• 7.5A Combined: Turn Left Front/Side (C3-N), Turn Left Rear (C1-G), Trailer Turn Left (C2-H), Turn Right Front/Side (C3-R), Turn Right Rear (C1-P), Trailer Turn Right (C2-E)
• 6.7A Combined: Left Backup Lamp (C1-A), Right Backup Lamp (C1-J), Backup Alarm (C1-H), Right Low Beam (C3-L), Right High Beam (C4-K), Left Stop Lamp (C1-N), Right Stop Lamp (C1-L)
• 6.7A: Right DRL (C3-K), Left DRL (C4-F)
• 6.7A Combined: Optional Fog/Road Lamps (C3-C, C3-D)
• 0.85A: AMU Solenoid #0 (C5-H), AMU Solenoid #1 (C5-J), AMU Solenoid #2 (C5-L), AMU Solenoid #3 (C5-M)
• 0.2A: Trailer Power Relay (C2-A)

*Maximum allowable combined current load when turn signals are flashing.

The CHM has connectors C1 (Tail Light), C2 (Trailer Module), C3 & C4 (Forward Chassis), and C5 (Air Management Unit). Detailed pinout tables are provided for each connector.

Multiplexing System

The term "multiplexing" refers to how the Business Class® M2 electrical system sends multiple electronic messages through the same signal path simultaneously via data links.

The system uses two primary data links:

• J1939 Datalink (High speed): A high-speed vehicle communications network allowing devices to broadcast and receive information. Messages include identifiers for priority and sender. Terminating resistors are used at each end.
• J1708/J1587 Datalink (Low speed): A low-speed datalink for network protocol and simple information exchange, including diagnostic data.

Multiplexing System Backbone: The J1939 backbone wiring connects components like CHM, ABS, TCU, BHM, AGS, MBE, ICU, and Diagnostic Connector. The J1708/1587 datalink connects similar components via a dash junction block.

Terminology:

• Backbone: Main J1939 wiring between terminating resistors, excluding branch circuits. Max recommended length between nodes is 3 meters, branch length 1 meter, total backbone 30 meters.
• Branch Circuit: Section of J1939 datalink between the backbone and control units or diagnostic connector.
• Diagnostic Connector: A 9-pin connector for troubleshooting.

System Tap Points: Details dash tap points for Ignition Accessory Power, Ground, and Dash Illumination. It also describes J1939 and J1708/1587 datalink connections, including the importance of terminating resistors and how to connect to the J1939 network for body builders.

Component Module Locations are listed with corresponding module numbers for J1939 harness drawings.

Switches

Low Current Smart Switches: These switches use voltage signals to communicate with the BHM, indicating their function and state (on/off). They are identified by unique resistor combinations.

• Two-position switch: Provides an on/off signal.
• Three-position switch: Provides up/down/off signals.

Common faults include Extra Smart Switch (unprogrammed), Duplicate Smart Switch (multiple identical switches), and Missing Smart Switch (programmed but not installed).

Smart Switch Pinouts are provided for two-position and three-position switches, detailing circuit numbers and descriptions.

860-004 SMART SWITCH EXPANSION MODULE (SEM): Available when more than five smart switches are installed, the SEM adds support for up to 6 additional smart switches per module (system supports up to 4 SEMs). Its function is to read, transmit, and control smart switch data on the J1939 datalink.

High Current Switches: These are factory-installed, switch-controlled power provisions for optional features like lighting. They mount on the dash, are fuse-protected, and provide blunt cut wires. They are commonly used for battery-powered lighting (dome, spot, beacon) or to enable other features.

• Module 329 Options: Lists various configurations of illuminated and extra switches with indicator lamps.
• Optional Power Switches: Extra switches can be ordered, mounted on the dash, and feature LEDs for illumination and position indication. They receive fused power up to 15A from the PDM.
• Connecting a switch using a chassis Junction Block: Switches can be pre-wired to a junction block near the CHM. The red wire receives power from the optional switch's output circuit. The PDM fuse for the optional switch is rated at 15A and should not be exceeded by the combined load.

Optional-switch Current Capacity tables detail PDM fuse ratings and switch output current capacity for different switch configurations.

High Current Switch Schematics

Wiring diagrams illustrate the configurations for high-current switches:

• Four-switch Configuration Wiring Diagram: Shows four dash-mounted switches, their connections to power (Battery B+), illumination, and ground, with associated fuses (F25, F26) and splice packs.
• One-switch Configuration Wiring Diagram With Junction Block and market light feed: Details a single switch connected via a junction block, including power, illumination, and connections to marker lights and the chassis module.
• One-switch Configuration Wiring Diagram Without Junction Block: Illustrates a single switch connected directly, showing power, illumination, and ground connections.

Tail Lights

This section details various tail light configurations and connection options for body builders.

Tail Lights and Connections: Body builders can order connector-only options or use specific data codes (353) for lighting interfaces.

Wiring Only Options:

• Combination Stop/Turn/Tail, Separate Backup Light (294-090): Omit stop/tail/backup lights, provide wiring for combined stop/turn lights up to four feet beyond the frame end.
• Combination Stop/Tail, Separate Turn, Separate Backup Light (294-046): Omit stop/tail/backup lights, provide wiring with separate stop/turn wires up to 4 feet beyond the frame end.
• Combination Stop/Tail, Separate Turn, Separate Backup Lights (294-094): Omit stop/tail/backup lights, provide wiring with separate stop/tail wires up to 7 feet beyond the frame end.

Tail Light Configurations:

• Combination Stop/Turn/Tail/Backup Lights: Integral units (294-001, 294-017).
• Combination Stop/Turn/Tail, Separate Backup Lights: LED Combination (294-042) or Incandescent Combination (294-002).
• Combination Stop/Tail, Separate Turn, Separate Backup Lights: Truck-lite 3-chamber modules (294-021).

Tail Lights Detail: Provides pinouts for the CHM Connector C1 and rear light connectors (separate stop/turn, combination stop/turn). It includes detailed wiring diagrams for integrated and individual rear lights.

Engine & Transmission Interface

Engine Interface: Freightliner provides an engine interface harness for optional body builder features like PTO applications, offering options for fast idle, increment/decrement, multiple fixed speeds, and variable RPM. Data book codes (Mod 148, 163, 87L) specify remote engine throttle types, interface connector locations, and interlock requirements.

Transmission Interface: This harness provides connections for 1000/2000 Series or 3000/4000 Series electronic controls, including optional I/O circuits and the speedometer signal. It features a front wall connector for body builder use.

Detailed pinout assignments and data book codes are provided for both engine and transmission interfaces, including specific Allison Transmission Functions.

Body Builder Lighting Interfaces

This section covers vehicle interface lighting options and body builder lighting connectors.

Vehicle Interface Lighting: Options include wiring with body builder connectors mounted at the back of cab, end of frame, or with PDM integration.

Body Builder Lighting Interfaces:

• Low Current Options: Specify current per side for stop lamps, turn lamps, backup lamps, and marker lamps, with connection points.
• High Current Options: Specify higher current ratings per side and combined options, with connection points at the back of cab or end of frame.

High-current Lighting Interface Harness (A06-48218): Details connector pin assignments, signal names, types, circuit colors, numbers, and current capacity for high-current lighting. Includes a diagram showing connections to relays and the chassis module.

Low-current Lighting Interface Harness (A06-44388): Details connector pin assignments, signal names, types, circuit colors, numbers, and current capacity for low-current lighting. Includes a diagram showing connections to the chassis module.

Trailer Electrical System

This section details various trailer connectors and wiring diagrams for the trailer electrical system.

Trailer Connectors: Descriptions are provided for primary connector/receptacle types, including SAE J560 7-way connectors mounted at different locations (end of frame, back of cab, LH deck).

Wiring Diagrams: Diagrams illustrate the trailer electrical system with both J560 and ISO 3731 connectors, or with only a J560 connector. These diagrams show the connections for trailer power relay, tail lamp relay, turn lamp relays, stop lamp relay, marker lamp relay, and their integration with the chassis module and ABS controller.