Ignition Switch Wiring for the Bobcat 853: Troubleshooting, Replacement, and Practical Insights

[MikePhua]

Understanding the Bobcat 853 Electrical Architecture
The Bobcat 853 skid-steer loader, like many compact construction machines of its era, relies on a relatively simple 12-volt DC electrical system to manage critical functions such as starting, fuel delivery, lighting, and safety interlocks. At the heart of this system lies the ignition switch—a multi-position rotary switch that controls the flow of power to various circuits.
This ignition switch is not merely a “keyed” on/off switch but a four-position component controlling multiple operational phases:

• OFF: All circuits are disconnected
  
• ACC (Accessory): Powers lights and auxiliary systems without engaging ignition
  
• ON (Run): Powers the fuel solenoid, gauges, and safety circuits
  
• START: Sends voltage to the starter solenoid to engage the engine
  

The switch essentially acts as a distribution node, channeling current from the battery to the appropriate systems depending on its position. Problems with the ignition switch or its wiring can cripple the machine entirely.
Typical Wiring Layout and Color Codes
Bobcat’s standard wiring scheme uses color-coded wires to simplify troubleshooting and replacement. On the 853, ignition switch terminals usually include:

• B (Battery / Power Input): Usually Red – constant 12V from battery
  
• S (Start / Starter Solenoid Output): Usually Yellow or White/Red – hot only during “Start”
  
• A or I (Ignition / Accessory): Usually Black or Purple – hot in “Run” and “Start”
  
• G (Ground): Sometimes Black or Green – not always present on all switch models
  
• L (Lights / Accessory): May be Orange – used in “ACC” or “Run” positions
  

Some Bobcat models also use a “R” terminal for choke control or fuel cutoff, depending on the engine type. The wires often run through a harness bundled with weatherproof connectors and fuse protection.
Common Ignition Switch Issues
Failures in the ignition system are a frequent source of downtime in older skid steers like the 853. Common symptoms include:

• Machine won’t crank
  
• Starter clicks but does not turn
  
• No dash lights or gauges when key is turned
  
• Engine cranks but doesn’t start (fuel solenoid not energized)
  
• Power cuts out randomly while operating
  

Typical causes of these issues include:

• Worn internal switch contacts: From years of cycling under load
  
• Broken or corroded terminals: Especially if exposed to moisture
  
• Frayed or cracked wires: Due to vibration and rubbing inside the dash
  
• Blown fuses: Often a symptom of deeper shorts
  
• Improper switch replacement: Aftermarket or non-OEM switches with incorrect pin layouts
  

A construction crew in rural Arizona once spent days trying to diagnose a no-start issue on their 853 loader. The culprit? A cracked ignition terminal that only failed under vibration. Once replaced, the machine roared back to life.
Steps to Diagnose and Replace the Ignition Switch
1. Disconnect Battery
Always begin by removing the negative battery cable to prevent accidental shorts or sparks.
2. Access the Dash Panel
Remove the plastic dash cover to expose the ignition switch. Most 853s have a simple bolt-on cover retained by Phillips or Torx screws.
3. Label Wires Before Removal
Use masking tape or a photo to mark each wire position on the old switch. Even experienced techs can mix up terminals, especially if aftermarket parts don’t match OEM labels.
4. Test with Multimeter
Use a multimeter to check continuity between terminals in each key position:

• OFF: No continuity
  
• ON: B → I (and sometimes L)
  
• START: B → S (also I in some models)
  

If the expected voltage is absent at any output when the key is turned, the switch is faulty.
5. Replace the Switch
Install the new switch using the same wiring layout. Torque the mounting nut securely but avoid over-tightening to prevent cracking the plastic body.
6. Verify Operation
Reconnect the battery and cycle the key through all positions, verifying:

• Power at gauges and fuel solenoid in “ON”
  
• Crank in “START”
  
• No power with key “OFF”
  

If replacing with a non-OEM switch, compare resistance values and continuity patterns to ensure compatibility. Some universal switches may not match the Bobcat's needs precisely.
Wiring Repair Tips

• Use heat-shrink connectors or weather-rated crimp terminals
  
• Avoid electrical tape as a long-term fix
  
• Route wires away from sharp edges and moving parts
  
• Bundle with zip ties and leave slack for vibration tolerance
  
• Fuse inline power leads according to spec (typically 15-20 amps)
  

Preventative Practices for Electrical Longevity
Given the harsh environment in which Bobcats often operate, electrical reliability is paramount. Best practices include:

• Regularly inspect under-dash wiring for chafing
  
• Use dielectric grease on terminals to prevent corrosion
  
• Keep the ignition switch dry and protected—seal leaks around the dash
  
• Avoid high-pressure washing near the dash area
  
• Start machines monthly in the off-season to cycle electrical loads
  

A rental yard in Minnesota instituted a policy of replacing ignition switches every 3 years on all skid steers due to frequent failure from frozen condensation and salt exposure. This preventative maintenance reduced their no-start calls dramatically.
Stories from the Field: A Quick Fix That Saved a Job
A small landscaping contractor was facing delays on a city sidewalk prep job when their Bobcat 853 wouldn’t start. The machine had power to the lights but no crank, and replacing the starter yielded no results. A quick check of the ignition switch revealed that the start wire (yellow) had corroded off its spade terminal inside the connector shell. Using a spare terminal and crimp tool from his pickup, the operator restored function in 15 minutes—just in time for the concrete crew to pour.
Conclusion
Though compact and often overlooked, the ignition switch on a Bobcat 853 is a cornerstone of the machine’s operation. Understanding its wiring, behavior, and potential points of failure empowers owners and mechanics alike to maintain uptime and avoid costly delays. With clear diagnostics, simple tools, and a bit of patience, even a seemingly complex no-start issue can often be resolved with a few wires, a key, and some knowledge.