FAW Combination Switch Logic Assembly: A Critical Analysis of 6 Core Components

Welcome to this critical technical guide on the FAW Combination Switch Logic Assembly (Assembly 559). This is the complete, multi-function, steering-column-mounted control unit for the FAW Jiefang CA4251P66K24T1A3E5 6×4 diesel semi-trailer tractor. This is the primary tactile “command center” for all of the truck’s vital driving functions, including lights, turn signals, wipers, and cruise control.

The FAW Combination Switch Logic Assembly is a complex electronic and mechanical “logic” hub. Its function is to consolidate multiple driver inputs into a single, ergonomic unit. This assembly includes the ‘Headlight & cruise control switch assy’ (3735035-61B) and the ‘Wiper & exhaust brake switch assy’ (3735040-61B), which act as the “stalks” or “levers.”

This in-depth guide is an essential resource for professional diesel technicians and electricians. We will deconstruct the entire FAW Combination Switch Logic Assembly into its 6 serviceable components, explaining the critical “logic” of each switch, its function in controlling the ECU and vehicle systems, and the ‘Clock spring mounting bracket assy’ (3735045-61B) that secures it. A fault in this FAW Combination Switch Logic Assembly can affect everything from the headlights to the exhaust brake.

Core Component 1: The ‘Combination Switch Assembly’ (3735010-61B)

The heart of the FAW Combination Switch Logic Assembly is the ‘Combination switch assembly’ (3735010-61B). This is the main “body” or “housing” of the unit, which mounts directly to the truck’s steering column. This component is the central “logic” hub.

Its “logic” is twofold:

1. **1. Mechanical Hub:** It provides the physical mounting points and pivot mechanisms for the two main control stalks (the headlight switch and the wiper switch). It is designed to provide a tactile, reliable “click” for each position, ensuring the driver can operate it by feel without taking their eyes off the road.
2. **2. Electrical Interface:** This housing contains the “clock spring” (or connects to it). The clock spring is a clever “logic” device, a “spooled-up” flat ribbon cable that allows the steering wheel (and the buttons on it, like the horn) to turn continuously while maintaining a constant electrical connection to the main wiring harness. This ‘Combination switch assembly’ is the non-rotating base that the clock spring feeds into.

All the electrical signals from the stalks of the FAW Combination Switch Logic Assembly are routed through this main body, into a single, large multi-pin connector. A failure in this main housing, such as a cracked pivot point or a failed internal connector, would necessitate the replacement of the entire FAW Combination Switch Logic Assembly.

Core “Logic” 2: ‘Headlight & Cruise Control Switch’ (3735035-61B)

The ‘Headlight & cruise control switch assy’ (3735035-61B) is the left-hand “stalk” of the FAW Combination Switch Logic Assembly. This single lever provides the “logic” for two unrelated, yet critical, systems.

**Lighting Logic:** This is the truck’s main light controller. The driver uses this stalk to:

• **Twist (Rotary Switch):** Select “Off,” “Parking Lights,” or “Headlights (Low Beam).”
• **Push/Pull (Lever):** “Flash” the high beams (momentary) or “latch” the high beams on.
• **Up/Down (Lever):** Activate the left and right turn signals (indicators).

**Cruise Control Logic:** This stalk also contains the buttons for the cruise control system. These buttons (e.g., “On/Off,” “Set/Accel,” “Resume/Decel”) do not send power; they send low-voltage “logic” signals directly to the truck’s ECU. The ECU then interprets these signals and takes over the electronic throttle to maintain a set speed. This integration is a key part of the FAW Combination Switch Logic Assembly‘s ergonomic design.

A failure of this stalk in the FAW Combination Switch Logic Assembly is a major safety and compliance issue. Worn contacts can lead to flickering headlights, turn signals that don’t cancel, or an inoperative cruise control system.

Core “Logic” 3: ‘Wiper & Exhaust Brake Switch’ (3735040-61B)

The ‘Wiper & exhaust brake switch assy’ (3735040-61B) is the right-hand “stalk” of the FAW Combination Switch Logic Assembly. This lever controls visibility and, most importantly, auxiliary braking.

**Wiper/Washer Logic:** The rotary switch on this stalk provides the “logic” for the windshield wipers. It allows the driver to select:

• **Intermittent:** Activates the wiper on a timed delay (e.g., every 5 seconds).
• **Low Speed:** Constant low-speed wipe.
• **High Speed:** Constant high-speed wipe for heavy rain.
• **Washer:** A momentary-push button that activates the washer fluid pump and triggers a single wipe.

**Exhaust Brake Logic:** This stalk’s most critical “logic” is the “exhaust brake” (or “jake brake”) control. When the driver activates this switch (often by pulling the lever), it sends a signal to the ECU. The ECU then commands a “butterfly valve” in the exhaust manifold (see Assembly 128) to close. This “plugs” the exhaust, turning the massive diesel engine into a powerful air compressor. This “engine braking” “logic” allows the driver to control the truck’s speed on long-downhill grades *without* using the service brakes (the foot pedal). This prevents the service brakes from overheating and failing (“brake fade”).

A failure of this switch in the FAW Combination Switch Logic Assembly can be catastrophic. If the wipers fail, the truck is unusable in the rain. If the exhaust brake fails, the driver risks a runaway-truck scenario on a steep grade. This makes the FAW Combination Switch Logic Assembly a primary safety component.

The Mounting and Support System

The FAW Combination Switch Logic Assembly must be mounted rigidly to the steering column. This is the function of the ‘Clock spring mounting bracket assy’ (3735045-61B).

This bracket is the “foundation.” The main ‘Combination switch assembly’ (3735010-61B) is bolted to this bracket, which is then clamped to the non-rotating part of the steering column. This ensures that the FAW Combination Switch Logic Assembly remains stationary while the steering wheel rotates around it.

This entire assembly is secured with ‘Cross recessed pan head self-tapping screw’ (CQ2782913) and ‘Cross recessed pan head screw assembly’ (Q2360520) fasteners. The “assembly” (combination) screws have pre-installed lock washers, a “logic” that prevents them from vibrating loose over time. A loose FAW Combination Switch Logic Assembly would feel “cheap” and “flimsy” to the driver and would eventually fail from the vibration and stress.

FAW Combination Switch Logic Assembly Parts List

The following table provides the complete, detailed breakdown of all 6 components identified in the ‘Combination Switch Logic Assembly’ (559) diagram for the FAW CA4251P66K24T1A3E5 tractor.

Technical Specifications and Assembly Context

The specifications for the FAW Combination Switch Logic Assembly are defined by its function as the all-in-one electronic and mechanical control stalk system. The FAW Combination Switch Logic Assembly is a key component of the driver’s interface.