Here are results
Headlight on measured at connection 11.2v
Battery 12.2
Regulator Black Green 11.6v
Hope that helps
I suspect you may be giving me voltage readings under different engine run conditions. And, that will throw the following analysis off base. Here is an analysis summary if you don't wish to read the technical justification below. Clean all your connectors and switch contacts on your bike, and you should be able to live with the bigger headlight. You will also find that you new or old headlight is far brighter than you can see now.
1 - A 12.2Volt battery is not fully charged.
2 - You are losing 1 Volt between battery and headlight.
A 55 Watt headlight rated at 12.8 volts would have a filament resistance of 2.98 ohms. (P/E = I, E/I= R, or)
Feeding 11.2 Volts to it will make it behave as a 42 watt bulb drawing only 3.75 Amps. (E/R = I, I*E=P)
The entire headlight circuit is drawing 3.75 Amps, so a 1 Volt drop in wiring, connectors and switches, between power source and H/L means there is an extra 2.66 ohms in those pathway components. (E/I = R) comsuming an extra 3.75 Watts.
Where's the resistance?
A quick online search found that 18 ga wire has a resistance of about .006 ohms per foot. Even if there were 10 feet of wire between battery and H/L that contribution should only be .06 Ohms.
That leaves connector terminal resistance and and switch contact resistance. When new, these contacts have a resistance of about 0.01 ohms for each contact. However, unless the contacts are made of noble metals, they begin to oxidize (for the connectors) and carbonize, in the case of current carrying switch contacts that flash when making/breaking a circuit.
You can count the connections in the path between H/L and battery. But, assuming there were ten of each (20 total), that would only be 0.2 ohms, for a total circuit resistance when new of about 0.26 ohms. Your bike has demonstrated ten times the expected resistance. It is unlikely it is limited to just the headlight circuits, it is more likely endemic to the entire bike. Find the bad connections and fix them.
Your charging system:
If your regulator is seeing 11.6 V across Black and green, it should believe that your battery is low and needs all the power the alternator can make. It should pass every bit of the voltage from the Black to the white wire which drives the alternator field strength. In an earlier report you indicated the regulator was seeing 13.5 volts at its input (battery near full) and the regulator was passing all but 4 volts to the alternator field (and rightly so). The less voltage delivered to the alternator, the less power it makes. The voltage regulator can't pass any more than it receives from the black wire. If that voltage is low, as in your latest reported case, then the alternator output will be correspondingly low. The very same connector and switch resistance that dim the headlight from low voltage, also diminishes alternator output. If the connectors and switches are wasting 10 percent of the energy produced by the alternator as heat, the alternator peak output effectively diminishes from 210 watts peak to 190 Watts peak. If the voltage being delivered to the regulator is 10% low, then the alternator real output diminishes 10%, making it an effective 170 watt capability. Adding more wattage for lighting, also diverts the effective output for charging the battery, and you will have to spend more time in the higher RPM band to have a hope of achieving battery restoration.
Good luck on your repair efforts!
Cheers,
