Swapping parts between different car models and generations can sometimes lead to unexpected electrical issues. One common scenario faced by Honda enthusiasts involves installing an older OBD1 alternator, particularly on a B16 engine setup, into a newer OBD2 vehicle. This article delves into a real-world problem encountered during such a swap and explores potential causes for dimming lights after the installation.
The issue arose in a 1996 Honda Civic (EK) originally equipped with an OBD2 system. After the original alternator on this EK Civic seized, a replacement “used” OBD1 alternator was sourced. Upon receiving the part, it was discovered that the connector was different – a round OBD1 style plug instead of the OBD2 connector.
To overcome this incompatibility, a custom conversion harness was fabricated using a salvaged OBD1 engine harness. By referencing wiring diagrams for both OBD1 (92-95) and OBD2 (96-00) Civics, the following wire mappings were established:
OBD1 Alternator Wiring
- Black/Yellow: Fuse box, Ignition
- White/Blue: Fuse box, Indicator light, Ignition
- White/Yellow: ECU (A21 pin)
- Blue: ECU (C5 pin)
OBD2 Alternator Wiring
- Black/Yellow: Fuse box, Integrated Control Unit
- White/Blue: Fuse box, Hot on Start
- White/Green: ECU, Alt Output Signal
- White/Red: ECU, Alt FR Signal
Conversion Harness Wiring
| OBD1 | OBD2 |
|---|---|
| Black/Yellow | Black/Yellow |
| White/Blue | White/Blue |
| White/Yellow | White/Green |
| Blue | White/Red |
After creating the conversion harness and connecting the OBD1 alternator to the OBD2 Civic, a peculiar problem emerged: the car’s lights – dome light, cluster lights, and headlights – began to dim on and off constantly. This rhythmic dimming was noticeable even while driving, resembling a headlight flashing effect to other drivers at night. Despite this electrical anomaly, the engine performance seemed unaffected, and the car ran normally.
To rule out mechanical issues, the pulley size of the replacement OBD1 alternator was compared to the original OBD2 pulley. Both pulleys measured 2.75 inches in diameter, eliminating the possibility of an underdrive pulley effect causing the dimming.
The question then becomes: what could be causing this intermittent dimming issue after an OBD1 alternator installation in an OBD2 system? Could there be differences in the amperage rating between OBD1 and OBD2 alternators that might contribute to this problem? Or could the issue lie within the wiring conversion or compatibility between the older alternator and the newer car’s electrical system? Further investigation is needed to pinpoint the root cause and find a solution to this perplexing electrical behavior.
