Complete Yamaha Big Bear 350 1992 Electrical Wiring Schematic
Start by isolating the ignition system circuits first–this model’s CDI module connections are prone to corrosion. Locate the stator output wires (typically yellow) and verify continuity between the engine case ground and each lead using a multimeter set to 200Ω. Readings above 0.5Ω indicate oxidized terminals; clean with 600-grit sandpaper or replace connectors with heat-shrink terminals rated for 20A.
The color-coded harness follows a standard pattern: red (20A main fuse), brown/white (ground), green/red (AC lighting coil), and blue (headlight switch output). Trace the brown/white wire from the ignition switch to the frame ground–interruptions here cause intermittent stalling. Secure all chassis grounding bolts with star washers and dielectric grease to prevent voltage drop under load.
For LED upgrades, bypass the stock regulator-rectifier with a 3-phase bridge rated for 50A. Connect the new unit’s DC output directly to a 12V auxiliary fusebox using 12-gauge silicone wire. Install a 30A inline fuse between the battery positive and the new fusebox to protect against short circuits during trail rides.
Check the kill switch circuit with the engine running–jumper the switch wires (black/white and black) to confirm operation. If the engine cuts out, replace the switch; store spares since aftermarket replacements often fail within 18 months. Label all splices with heat-shrink tubing and use crimp connectors (not solder) for vibration resistance.
Verify the starter solenoid operation by probing the small trigger wire (purple) with 12V–listen for a distinct click. No click means internal pitting; rebuild with new contacts or upgrade to a continuous-duty solenoid for winch applications. Keep the battery terminals coated with anti-corrosion gel; sulfation buildup reduces cranking amps by 30% in subzero conditions.
Electrical Schematic Guide for the 1993 ATV Model
Locate the main ignition switch connector near the steering column–pin assignments are critical. Terminal 1 (red/white) links to the battery via a 30A fuse, while terminal 3 (black/white) grounds the system. Skipping this step risks frying the CDI unit, which operates at 5V and triggers the ignition coil’s primary circuit. Use a multimeter to verify continuity before reconnecting.
Trace the charging circuit from the alternator to the rectifier-regulator–stator outputs three yellow wires (AC current) converted to DC. The regulator’s red wire (12V output) feeds the battery; black wires must ground to the frame. If voltage drops below 12.8V at idle, inspect the stator’s resistance (should read 0.2-1.0 ohms per phase) or replace the unit if readings exceed 5 ohms.
Key Component Pinouts
- CDI Unit:
- Black/white – ground
- Green – kill switch input
- Blue – ignition pulse from pickup coil
- Red – 12V supply
- Starter Relay: 85 (trigger), 86 (ground), 30 (battery), 87 (starter solenoid)
- Headlight Switch: Orange (high beam), white (low beam), black (ground)
Inspect the wiring harness for brittle insulation or corrosion–focus on junctions behind the dash and near the engine. Apply dielectric grease to connectors after cleaning with contact cleaner. For intermittent faults, wiggle test each wire while monitoring voltage at the CDI; a drop below 10V indicates a break. Replace the entire harness if more than three wires show damage; patching risks future failures.
Identifying Critical Electrical Connections on Your Vintage ATV
Start beneath the seat–specifically, near the fuel tank’s rear. The main fuse block, a black rectangular unit with three blade-style fuses, sits adjacent to the battery tray. Label each fuse by amperage (10A, 15A, 20A) to cross-reference later with the service manual’s circuit map. If corrosion is present, scrub the terminals with a wire brush and apply dielectric grease to prevent future oxidation.
The ignition switch harness emerges from the frame’s left side, bundled in a split-loom sleeve. Trace the six-wire cluster: red (constant power), black/white (ground), orange (accessory), yellow (ignition), blue/white (starter solenoid), and green/white (neutral safety). Secure connections with crimp connectors–avoid solder alone, as vibrations can fracture joints over time. Use a multimeter to verify voltage: 12.6V at red when the key is off; 12.6V at yellow when turned to “ON”.
Locate the CDI box, mounted under the front fender on the right side. Its four-pin connector (black, white/red, orange, green) interfaces with the stator and spark plug. Check for brittle insulation–replace the entire harness if cracking is visible. The stator wires (yellow and white) exit near the left crankcase cover; test resistance (0.2–1.0 ohms between phases) to confirm functionality. A reading outside this range indicates coil failure.
Sensor and Solenoid Placement
The engine temperature sensor threads into the cylinder head’s rear, featuring a two-wire lead (green and black). Disconnect it before removing the radiator; coolant remnants may short the connection. The neutral switch, a brass cylindrical component near the gearshift lever, uses a single green wire–clean its contact surface if false neutral readings occur.
The starter solenoid, a cylindrical unit with two large terminals, bolts to the frame above the right footpeg. The thick red wire (battery positive) attaches to the solenoid’s input; a thinner purple wire (from ignition switch) activates the coil. Test by bridging the terminals with a screwdriver: if the engine cranks, the solenoid is functional–if not, replace the contacts or entire unit.
Front and rear brake light switches hide near their respective levers. The front switch (left handlebar) has a gray/red wire; the rear (brake pedal) uses brown/white. Both require precise adjustment–gap between plunger and lever arm should be 0.5–1.0mm when brakes are released. Misalignment causes premature bulb failure or lighting flicker.
Examine the rectifier/regulator, a finned aluminum block tucked behind the left side panel. Its five-wire harness (two yellows, one red, one white, one green) manages charging output. Desolder and replace diodes if the battery drains overnight–alternator AC voltage should read 13.5–14.5V at 3000 RPM. Voltages below 13V suggest rectifier failure.
Inspect ground points carefully: a primary strap connects the battery’s negative terminal to the frame near the airbox. Scrape paint from attachment surfaces and re-secure with star washers to ensure conductivity. Loose grounds create intermittent electrical faults–symptoms include dim lights or erratic gauge readings.
Step-by-Step Tracing of the Ignition System Wires
Locate the ignition coil near the engine’s front, identifiable by its two thick wires–one leading to the spark plug, the other connected to the CDI unit. Disconnect the battery’s negative terminal before handling any electrical components to prevent short circuits. Use a multimeter set to continuity mode to verify the coil’s primary and secondary circuits.
The CDI (Capacitor Discharge Ignition) box is typically mounted beneath the seat or near the battery. Trace the thin black wire from the ignition coil’s negative terminal to the CDI–this is the pulse trigger. The CDI’s positive input comes from the stator via a colored wire, often yellow or white with a stripe, depending on the model’s charging system configuration.
- Stator output wires: Three yellow wires indicate a three-phase AC output; a single yellow wire may connect to a voltage regulator.
- CDI power input: A red or orange wire supplies 12V from the battery or ignition switch.
- Ground wires: Black with a green stripe or solid black, always terminating at the frame or engine block.
Follow the kill switch wire–usually red with a white stripe–for safety circuit tracing. This wire interrupts power to the CDI when activated. The ignition switch connects via a red wire to the CDI’s power input; if the engine fails to start, test this wire for 12V with the key in the “ON” position.
Testing Key Components
- Spark plug wire: Remove and inspect for corrosion; resistance should read 5,000–10,000 ohms.
- CDI pulse trigger: Disconnect and probe the coil-side wire–should show a brief voltage spike when cranking.
- Stator resistance: Measure between each yellow wire pair (0.5–2 ohms) and ground (~infinite resistance).
If the ignition system fails to fire, bypass the kill switch temporarily by jumpering its red/white wire directly to the CDI’s power input. For intermittent issues, wiggle-test each connection while monitoring voltage; frayed or loose terminals often cause misfires. Replace any wire with melted insulation immediately–this indicates overheating from poor grounding or excessive resistance.
The pick-up coil inside the stator generates the pulse signal. If the engine stalls or struggles to start, test its resistance (typically 200–500 ohms) between the black wire from the CDI and the stator’s ground. No continuity here means a faulty pick-up coil, requiring stator replacement. Always reconnect the battery’s negative terminal last after completing repairs.
Identifying and Testing the Charging System Connections
Begin by locating the stator output wires, typically bundled in a three-wire harness exiting near the engine’s left side cover. These wires–usually yellow with stripe variations–carry AC voltage generated by the stator’s coils. Verify their insulation for cracks or burns; damaged wires cause intermittent charging failure. Use a multimeter set to AC voltage (20V range) to measure output at idle: connect probes to any two stator wires and expect 12–18V. If readings drop below 10V, suspect stator or rotor issues.
The regulator-rectifier plays a dual role: converting AC to DC and capping voltage at ~14.5V to prevent battery overcharging. To test, probe the red DC output wire (often connected to the battery positive) with the multimeter in DC mode. With the engine running, voltage should stabilize between 13.8–14.8V. A reading below 13V indicates rectifier failure; above 15V suggests regulator malfunction. Check for corroded connectors on the unit’s heatsink–clean with electrical contact spray if necessary.
Step-by-Step Continuity Checks
| Component | Test Points | Expected Result | Failure Indication |
|---|---|---|---|
| Stator Coils | Any two stator wires | 0.1–0.5 ohms | OL (open circuit) or >2 ohms |
| Rotor (Field Coil) | Slip ring terminals | 2–6 ohms | OL or <1 ohm |
| Ground Path | Regulator case to engine block | 0 ohms | >0.5 ohms |
Disconnect the battery before testing to avoid false readings. For stator coils, switch the multimeter to ohms (200 range) and measure resistance between each pair of yellow wires. A dead short (0 ohms) or infinite resistance signals a failed coil. Test rotor continuity by probing the slip rings–accessible after removing the cover opposite the stator. Confirm the field coil’s resistance matches the table; deviations require rotor replacement.
Trace the ground circuit from the regulator-rectifier’s mounting point to the engine block. Use the multimeter’s continuity mode to verify a solid connection (beep + 0 ohms). Corrosion or loose bolts at this point cause charging voltage drops visible as dim lights or slow cranking. Inspect the kill switch wiring–a frayed black-white wire here can mimic charging issues by grounding the ignition circuit. Secure all connectors with dielectric grease to prevent future oxidation.
If all components test within spec but voltage remains low, monitor battery voltage during a 15-minute ride. A healthy system will maintain or slightly increase charge, while a failing rectifier will show rapid voltage drops. Swap the regulator-rectifier with a known-good unit if diagnostics remain inconclusive–this is the most common failure point. Avoid revving the engine excessively during tests; stator damage accelerates above 6,000 RPM if disconnected from the battery.