FAW Start Switch: A Critical Analysis of the 2 Core Components That Power Your Engine

Welcome to this critical technical guide on the FAW Start Switch (Assembly 558). This is the complete, driver-operated, “key-in” ignition control assembly for the FAW Jiefang CA4251P66K24T1A3E5 6×4 diesel semi-trailer tractor. This component is the primary authorization and power-up command for the entire vehicle’s electrical and engine systems.

The FAW Start Switch is the “logic gate” for all vehicle power. Its function is to translate the physical rotation of the driver’s key into distinct electrical signals, providing power to different circuits (e.g., “Accessory,” “On,” and “Start”). It is a heavy-duty, multi-position switch designed to handle the demands of a 24-volt commercial vehicle system.

This in-depth guide is an essential resource for professional diesel technicians and electricians. We will deconstruct the entire FAW Start Switch assembly into its 2 serviceable components as listed: the main ‘Start switch assembly’ (3704010-A01) and the ‘Combination bolts’ (CQ1460830) that secure it. A faulty FAW Start Switch is a primary cause of no-start or intermittent electrical issues.

Core Component 1: The ‘Start Switch Assembly’ (3704010-A01)

The heart of this assembly is the ‘Start switch assembly’ (3704010-A01). This is the complete, dash-mounted ignition lock cylinder and the electrical switch that it controls. This FAW Start Switch is a robust component designed to handle the high electrical loads and constant daily use of a commercial truck.

This single component has two “logic” systems:

1. **1. Mechanical Logic (Security):** The lock cylinder itself. It is a pin-and-tumbler lock that will only rotate when the correctly-cut, unique key is inserted. This is the primary anti-theft “logic” of the FAW Start Switch, ensuring only an authorized driver can operate the vehicle.
2. **2. Electrical Logic (Power Distribution):** The “switch” part at the back of the cylinder. As the driver rotates the key, this switch connects the main battery power to different circuits in sequence.

A FAW Start Switch in a heavy-duty truck typically has four positions:

* **LOCK/OFF:** All power is disconnected. The steering wheel is often mechanically locked. * **ACC (Accessory):** This position provides power to “non-essential” circuits like the radio, windows, and cabin lights, without powering up the engine’s main ECU. * **ON (Run):** This is the main “run” position. This energizes all critical systems: the ECU, the fuel pump, the ABS computer, all dashboard gauges, and the emissions control modules (like the FAW Nitrogen-Oxygen Sensor Logic Assembly). * **START (Momentary):** This is the spring-loaded position. Turning the key here sends a 24V signal *not* to the starter itself, but to a “starter solenoid” or “relay.” This small signal from the FAW Start Switch is used to activate a high-amperage (1000+ amps) circuit that engages the starter motor (see Assembly 34) and cranks the engine.

Failure of the FAW Start Switch is a common diagnostic challenge. Worn internal contacts can lead to “intermittent power” (dash lights flickering, engine cutting out). A failed “START” contact will result in a “no-crank” condition: the driver turns the key, all the lights come on, but nothing happens. A failure in the “ON” circuit can prevent the ECU or fuel pump from energizing, resulting in a “crank-no-start” condition.

Core Component 2: The Fastener “Logic” (CQ1460830)

The second component listed for the FAW Start Switch assembly is the ‘Combination bolt’ (CQ1460830). The list calls for two. These are the fasteners that secure the ‘Start switch assembly’ to the steering column bracket (part of Assembly 535) behind the dashboard.

These are not standard bolts. Their “logic” is threefold:

1. **Security (Break-off Heads):** Often, ignition-securing bolts are “shear bolts.” They are tightened at the factory until the hex head “shears” or “breaks off,” leaving only a smooth, cone-shaped head. This makes the FAW Start Switch extremely difficult to remove by a thief, as there is nothing for a wrench to grip.
2. **Vibration Resistance:** The “Combination” (组合) designation means these bolts have a pre-installed, captive lock washer (like a “spring” or “star” washer). This is a critical “logic” feature in a high-vibration environment. This washer exerts constant spring tension, preventing the bolt from vibrating loose over time.
3. **Clamping Force:** These bolts provide the rigid, secure mounting that the FAW Start Switch needs. A loose switch would vibrate, causing premature wear to the electrical contacts and an annoying “rattle” in the dash.

The entire “logic” of the FAW Start Switch relies on it being a stable, secure, and authorized-access-only device. These specialized fasteners are what provide that security and reliability, making them a critical, non-optional part of the FAW Start Switch assembly.

FAW Start Switch Parts List

The following table provides the complete, detailed breakdown of all 2 component types (totaling 3 pieces) identified in the ‘Start Switch’ (558) diagram for the FAW CA4251P66K24T1A3E5 tractor.

Technical Specifications and Assembly Context

The specifications for the FAW Start Switch are defined by its function as the primary, key-operated power control unit for a heavy-duty 24V vehicle. The FAW Start Switch is a critical safety and security component.