Alternator FR Signal Test

Fig. 23 System checker harness terminal identification:

Exc. 1987-88 Accord & 1988 Prelude
1. Connect system checker harness between ECU and wire harness coupler.
2. Connect positive probe of voltmeter to terminal B14 (white/red) and negative probe to terminal A18 (black/red) of system checker harness, Fig. 23.
3. Start engine, then turn headlights on and off. Voltage should drop when headlights are on and rise when headlights are off, and voltage should be in the 0 to 5 volt range.
4. If voltage is not as specified, stop engine, check continuity of wiring between alternator and ECU and repair as needed.
5. If continuity is present, check for defective voltage regulator or alternator, and repair or replace as required. FR terminal diode is defective if continuity or no continuity exists in both directions between F and FR terminals of voltage regulator.