Often the stator has failed and the regulator gets the blame. A stator is difficult to check completely as they sometimes have thermal breakdowns that only fail when hot. On Turbos, stators live in a VERY hot environment. So, the best practice is frequent oil changes and to replace the stator every 20K miles. Along with cam chain and tensioner/guide blades and water pump seal this becomes the infamous “triple by-pass” on CX500s. The CX650s are harder on the starter drive parts, so those are also replaced at 20K as preventative maintenance …hence the “quadruple by-pass."
These simple checks will find some bad stators, but a stator that passes these checks may still be defective under load and heat.
Static Tests
1. Honda Turbos have a 3-phase, permanent magnet charging system. There are 3 yellow wires that connect from the stator to the rectifier / regulator. Check the resistance between the phases. This should be a very low value …under 1 or 2 ohms. Practically speaking, this is no resistance. The resistance between each of the 3 wire combinations (AB, AC, BC) should be equal. If you see higher resistance, or unequal resistances, the stator is bad.
2. Check the resistance of each yellow wire (phase) to ground, it should be well over 10 Meg ohms. Practically speaking, this is infinite resistance. Most multimeters will display "OL" or "open loop." If you get any value via this test, you have a ground fault and the stator is dead.
Dynamic Testing
Battery condition is important. No regulator can make up for a bad or weak battery. Have it load tested, or simply replace it if there is any doubt. Always start with a fully charged battery!
1. Temporarily disconnect both rectifier/ regulator connectors beside the battery.
2. Start the engine and test for AC voltage across each pair of yellow wires. You should see approximately 20 Volts (AC) across each pair of yellow stator wires at idle.
3. Test for AC voltage again. This time, slowly rev the engine to 5,000 rpms while observing the AC voltage. You should see a steady climb to approximately 100 Volts (AC) across each pair of yellow stator wires.
4. Reconnect the rectifier/ regulator connectors aand start the engine. Test for DC voltage at the battery. At idle, you should see approximately 13.8 - 14.5 Volts. This indicates a healthy charging system.
5. If you see values ouside of this range, the usual culprits are poor main ground, wiring fault or defective regulator.
General
1. All connections in a motorcycle’s charging system should be properly crimped. Crimping was invented by AMP Incorporated in 1941 as a “solderless” method for terminating wires and connectors in military applications. When done right, a crimped connection can be much stronger and longer lasting than a soldered connection. It should have equal electrical resistance to the equivalent length of wire alone!
2. Crimped connections are less susceptible to failure from vibration or fatigue. A properly done crimp is also gas-tight as well, not allowing oxidation to degrade it over time. Practically speaking, all Honda factory connections are crimped.
3. Use the right crimping tool and practice on scraps of wire to develop “feel” for the proper crimping technique.
4. The 2 block connectors at the rectifer / regulator should be opened, inspected and cleaned annually. After cleaning, I treat these connectors to a de-corrosion and preventative lubrication with an aviation product called ACF-50.