Here is a portion of the wiring diagram relative to the Estart bikes. Both lighting outputs go to the regulator/rectifier. The yellow wire is there for voltage regulation. The white wire is rectified to DC.
Based on info from Glenn and John, there can be only one ground, either for the AC system OR the DC system (when using a full wave rectifier).
On an estart bike, both systems are grounded. From this we know that the voltage regulator is a halfwave type creating a DC output for battery charging. The lighting runs on AC taken from the yellow wire.
TrailTech says not to ground the battery negative when using their reg/rect unit (most likely because of bikes that use an AC ground). In order to get the maximum DC output I believe I must remove the stator ground so the AC system is floating. That should allow me to keep the DC system grounded and use the TrailTech reg/rect for full output. The yellow wire would not be used anymore.
A friend with a lot of electronics experience just stopped by. He agrees that the rectifier is half wave and cautions that using a full wave rectifier on the white wire might not be wise. Based on the simplified GG wiring diagram, he is guessing that the AC voltage on the white wire might actually be ~24 volts.
The resistance (to ground) measures 0.8 ohms on both the yellow and white wires. The yellow (assumed to be the mid-point of the windings) is probably at ~12 volts. A full wave rectifier on the white wire might actually yield ~24VDC. Before doing anything else I need to find out what voltage is on both white and yellow wires with the engine running.
In reality 24VAC through a halfwave rectifier may not be much less energy supplied than 12VAC through a fullwave rectifier.
The unknown at this time is the actual winding connections on the stator. It might make more sense to create a common at the mid-point and feed both windings into a full wave rectifier.
There is always more to learn.