Spence, This link may help you: https://www.mac-pac.org/wp-content/uploads/2014/09/R1100RT-Elec-Diagram-V2_2.pdf Pins 1 & 3 on the O2 sensor connector are both ground pins. The measurements you’re making on the blue and white/blue wires seem correct. That O2 sensor error you’re getting, “shorted to ground”, means that at some time while you’re riding, the Motronic was unable to add enough fuel to reach stable Closed Loop, so the O2 voltage/AF-XIED stays below 450 mV. It could point to a weak O2 sensor (see if you get it while riding at lower AF-XIED settings) or it can point to a leaking in-tank hose which doesn’t allow quite enough fuel at higher power settings. It almost never points to an actual short to ground. And it doesn’t have anything to do with the heater.