Complete Wiring Diagram Guide for the 1991 Acura Integra Models
Begin with the main fuse box under the dashboard–this cluster houses critical relays and fuses for ignition, lighting, and accessory systems. Locate the 10A “ECU” fuse (position 15) and verify continuity with a multimeter; erratic voltage here disrupts fuel injection timing. For frequently failing tail lights, trace the brown/white wire from the bulb socket back to connector C105 behind the left kick panel. Corrosion at this junction is common, especially in vehicles exposed to coastal climates.
Alternator charging issues often stem from the white/red wire at terminal “B” on the alternator itself. Check for 13.5–14.5V at idle when probing this connection. The engine harness retains data from past short circuits–inspect the bundled section near the distributor (brown/black wire) for brittle insulation or melted terminals. Replace the entire segment if chafing is evident rather than splicing.
The instrument cluster harness uses a modular plug (20-pin); pin 18 (blue/white) carries the tachometer signal. If the gauge fluctuates or freezes, test resistance across this pin and ground–values should not exceed 2 ohms. Power window failure typically involves the breaker circuit (yellow/red wire at the door jamb switch). Bypass intermediate connections temporarily to isolate whether the fault lies in the motor, switch, or wiring.
For A/C compressor engagement problems, focus on the thermostatic switch (2-wire connector at the evaporator). The green/white wire must show 12V with ignition ON and the system activated. If absent, verify continuity through the pressure cycling switch (located on the accumulator) before condemning the compressor clutch coil. Stereo power issues often hide in the fuse link (10A “Radio”)–this circuit also feeds the cigarette lighter; both failing together is a telltale sign.
Electrical Layout for the ’91 Sport Compact: Hands-On Repair Tips
Start troubleshooting ground faults at connector E behind the dashboard’s lower panel. Disconnect the 10-pin plug, inspect terminals 3 (black/yht) and 9 (blu/blk) for corrosion–common failure points causing intermittent stalls. Clean with electrical contact cleaner, then verify continuity using a multimeter set to 200 ohms. Resistance above 0.5 ohms indicates damaged wiring needing replacement.
For ignition system issues, locate the main engine harness near the firewall. Focus on the orange/black (ORN/BLK) wire feeding the ignition coil. Check for voltage at the coil’s positive terminal with the key in the “ON” position; expected reading is 12V. If voltage is absent, trace upstream to fuse 17 (10A) in the under-dash fuse box–replace if blown, ensuring no short in the ORN/BLK line.
Headlight circuit problems often stem from the headlight relay. The relay (gray, labeled “A”) sits in the main fuse box under the hood. Swap with a known-good relay (e.g., horn relay) to test. If headlights function, the original relay is faulty. For persistent failures, inspect the light green/red (LT GRN/RED) wire at the dimmer switch for chafing against the steering column.
Audio system malfunctions typically involve the power antenna circuit. Access the antenna motor assembly behind the rear quarter panel. The motor’s green/yellow (GRN/YEL) power wire should show 12V when the radio is on–if not, check fuse 29 (7.5A) in the interior fuse panel. Additionally, verify the brown/white (BRN/WHT) ground wire’s connection to the chassis near the antenna base; corrosion here causes erratic operation.
Door lock actuators fail frequently due to wiring flex at the door hinge. Peel back the rubber boot between the door and body to expose the 6-wire harness. Look for broken strands in the light blue/yellow (LT BLU/YEL) and blue (BLU) wires–these power the motor in both directions. Solder any damaged sections, then protect with heat-shrink tubing. Reassemble carefully to avoid pinching the repaired wires.
Climate control issues often trace to the blower motor resistor block, mounted behind the glove box. The block’s red/black (RED/BLK), white (WHT), and green/white (GRN/WHT) wires regulate fan speeds. Use a test light to confirm 12V at the RED/BLK terminal with the ignition on and fan switch set to low. If voltage is present but the blower doesn’t operate, replace the resistor block–common failure for this model’s HVAC system.
Finding the Right Electrical Schematic for Your Early 90s Legend Coupe
Locate the VIN on the driver’s side dashboard near the windshield base or the door jamb sticker to confirm the exact trim and engine code–RS, LS, GS, or GS-R variants require distinct schematics. The B18A1, B18B1, and B17A1 powerplants each have unique sensor, ignition, and fuel injector pinouts. Factory service manuals categorize circuits by harness sections: under-dash, engine bay, and rear lighting clusters; mismatches here cause phantom voltage drops or erratic gauge behavior.
Key Harness Variations by Trim
- Base RS: Simplified two-wire oxygen sensor (pre-OBD-I), absence of rear window defroster relay, and three-terminal hazard flasher switch.
- LS/GS: Supplemental restraint system wiring for airbag deployment loops; verify continuity across yellow connectors near the steering column.
- GS-R: Dual-stage MAP sensor wiring incompatible with single-stage LS harnesses; incorrect splicing triggers P1300 code.
Use colored wiring guides–black/white stripe denotes ground, solid green indicates right-turn signals, and striped blue carries high-beam input. Avoid generic online diagrams; cross-reference with Honda’s PGM-FI supplement (section 22) for pin assignments at the ECU’s 26-pin connector, particularly terminals A10 (ignition coil trigger) and A20 (ECT sensor).
Step-by-Step Wire Color Codes and Connector Pinouts for Common Circuits
Locate the main engine harness near the firewall. The primary power feed for the ignition system uses a black/yellow (BLK/YEL) wire, typically terminated at fuse #15 (10A) under the dash. Verify continuity from the fuse box to the ignition switch (connector C101, pin 8) before proceeding. For ground circuits, follow the black (BLK) wires to their chassis connections–dirty or corroded grounds cause intermittent failures. Use a multimeter to confirm resistance below 0.5 ohms.
For fuel injection, trace the white/blue (WHT/BLU) wire from the main relay (connector C351, pin 1) to the fuel pump. The relay coil is triggered by a white/green (WHT/GRN) signal from the ECM (pin A16). If the pump fails, check for 12V at the relay output before assuming pump failure. Cooling fan circuits use green/white (GRN/WHT) (high speed) and blue/red (BLU/RED) (low speed), controlled by the temperature switch (connector C202, pin 1 and 2). Cross-reference readings with a scan tool to isolate switch faults.
Instrument Cluster Wiring Reference
| Function | Wire Color | Connector | Pin |
|---|---|---|---|
| Tachometer Signal | Blue/Yellow (BLU/YEL) | C104 | 10 |
| Fuel Level Sender | Yellow/Black (YEL/BLK) | C103 | 9 |
| Temperature Gauge | Green/White (GRN/WHT) | C102 | 1 |
| Parking Brake Indicator | Orange (ORN) | C105 | 6 |
| High Beam Indicator | Blue (BLU) | C105 | 7 |
Headlight circuits require special attention. The black/white (BLK/WHT) wire supplies low beams (connector C201, pin 4), while white/black (WHT/BLK) handles high beams (pin 5). Daytime running lights use a green/yellow (GRN/YEL) wire from the multifunction switch (connector C301, pin 3). If bulbs fail, inspect the combination switch first–corrosion here mimics bulb failure. For turn signals, follow the light green (LT GRN) (left) and gray (GRY) (right) wires from the flasher unit (connector C401) to each bulb socket.
Audio systems use a red/white (RED/WHT) power feed from the fuse box (fuse #21, 15A), routed through the ignition switch. Speaker wires vary by trim: standard models use pink (PNK) (front left), purple (PPL) (front right), gray (GRY) (rear left), and brown (BRN) (rear right). Premium systems add a separate amplifier with blue/white (BLU/WHT) for remote turn-on. Strip 5mm of insulation and solder connections–crimped splices corrode over time. For power windows, the pink/black (PNK/BLK) wire (connector C501, pin 1) carries the master switch signal; door motors use blue/white (BLU/WHT) for up and blue/yellow (BLU/YEL) for down.
Diagnosing Circuit Problems with Schematic Layouts
Locate the power distribution box in the engine bay–usually labeled “PDU” on the upper-left section of the electrical blueprint. Verify voltage at fuse inputs using a multimeter set to DC 20V. Expected readings: 12.4–13.2V at ignition-off, 13.8–14.7V when the engine runs. Deviations below 12V indicate a corroded terminal, blown fuse, or faulty alternator. Check fuse continuity first; replace if the resistance exceeds 0.5 ohms.
Step-by-Step Voltage Drop Test
- Attach the black probe to the negative battery post.
- Touch the red probe sequentially to each connector along the target circuit path while activating the relevant component (e.g., headlights, fuel pump).
- Acceptable drop: less than 0.2V per connection. Readings above 0.5V suggest high resistance–clean terminals with a wire brush or replace connectors showing green/copper oxidation.
- For grounds, measure from the component chassis ground to battery negative; ideal drop under 0.1V.
Trace color-coded lines on the schematic: solid red denotes constant power, yellow with stripe is ignition-switched, green controls lighting, black is ground. Follow the path from the fuse block to the end device. If the device activates but dims, suspect a loose crimp or corroded bullet connector–wiggle wires while monitoring voltage to isolate intermittent faults.
When diagnosing relays, remove the relay and jumper terminals 30 (power) to 87 (output) with a fused wire. If the component works, the relay coil or internal contacts are faulty. Test coil continuity between 85 and 86–should read 50–120 ohms; infinite resistance confirms an open coil.
- Check sensor resistance values against the legend:
- Coolant temp sensor: 2.2–2.7 kΩ at 20°C.
- Throttle position sensor: 0.5–1.5 kΩ closed, 4.5–6.5 kΩ wide open.
- O2 sensor: 0–1V lean, 0.9–1V rich.
- If readings are out of spec, disconnect the sensor and measure again–open circuit indicates internal failure.
- For actuators, apply 12V directly; a quiet click or no movement confirms a defective solenoid (fuel injector, purge valve).
Inspect printed circuit boards in modules for hairline cracks or burnt traces. Use a magnifying glass–suspect joints with dull, grainy solder. Reflow suspect pads with a 40W iron; add fresh solder if pad lifts. For modules housed beneath carpets, remove water intrusion sources first–seal firewall grommets with silicone grease before module replacement.