Update: see thread; ended up running a new wire from the battery. This went through a relay that used the old USB circuit as a positive trigger for a relay. This ensured the 12V socket was fully off when the ignition was off and had available 12V at up to 10amp power availabe.
The headlight circuit is linked to the ignition key and is only active when the motor is running. This makes it an ideal source both for greater available power and significantly reduced risk of parasitic draw draining the battery.
The existing wiring for the original glove-box USB only puts out a maximum of 14 Watts of power (14.1V at 1 amp). My phone-app reports only ~11 Watts maximum (14.1v at .806 amp real) actually makes it to my phone. This was fine for my old phone; but is just barely enough to trickle charge the new phone. The new phone requires around 25 Watts to stay charged while in active use (Navigation, music, ride-info, etc). This is not ideal for longer trips when I want to have the phone active while riding and not drain the battery to nothing.
The older halogen (Xenon?) headlights are reported to be using 55 Watts of power which means 12V at about 4.5 Amp. The OSRAM 67210CW LED bulbs I have installed now use just 14 Watts of power (14V at 1 Amp). That leaves a little more than 41 Watts (14V at ~3 Amp) available for accessories. That fits well within what the 36 Watts (14V at 2.6 amp) that newer USB power plugs can provide. The service manual says the headlights (on fuse 4) are a 15 Amp circuit that goes through a relay to power the headlights. Thats 15 Amp limit total but the combined USB + LED headlights would only add up to about 5 amps maximum.
12V socket. I used a Dremel to carefully make the old rectangle USB abrade away just enough plastic to make the square old USB cut out round to fit this.
The USB 12V plug; the little voltage LED is surprisingly useful on the bike.
⚠️ Last edited by pinheadh78 on UTC; edited 2 times