If you add a pair of headlight relays powered directly from the battery the current bypasses the normal headlight and you loose the Voltage drop.
If you use a larger headlamp bulb the Voltage drop increases pushing the battery Voltage higher still.
I'm in two minds as to this Voltage drop being a good thing, I know it will increase with time as the relay pins oxidize but drop back again if you wiggle the headlight relay.
You can read the Voltage drop directly if you measure from battery + to the black wire on the regulator, try it with the headlight On then Off, the engine doesn't need to be running. Then wiggle the relay, see if it changed. I get the sense the factory has wrestled with the charging over the years.
Some of the spine frame bikes like my VII Sport get a double dose of Voltage drop because the current passes through the start relay then the headlight relay. Other Guzzis just use the start relay to switch the headlight relay coil.
I have discussed with a few guys the possibility of moving the Voltage sensing to the ECU relay, the current there is much lower.
I think the main reason Luigi wired it this way, the regulator reference draws about 15 milliamps which is a significant drain on the battery, the later after-market direct connected regulators draw less than half a milliamp, still enough to flatten the battery over the winter.
BTW, make sure your DE regulator has an extra ground wire added, just a short one from the regulator to an engine bolt, the wire the factory provided all the way back to the battery is not adequate.
