singring said:
So, if you had a battery and a multimeter, how can you determine if the bike is +ve or -ve earth (ground)?
[Edit]Before attempting to connect the battery-
With the ignition switched off, and with the fuse in place, set the meter to Ohms, then connect one probe to earth/ground, and the other probe to the main ignition side battery wire terminal, if the meter registers a drop from infinity to low ohms with the
positive probe to ground, and a steady infinity (or close to infinity) reading when the probes are reversed, it's almost certainly a positive earth/ground system and will be the opposite for negative ground. If there's a drop in both directions then there could be short somewhere.
The simplest way would just be to check the polarity of the rectifier (+ stud), Zener and ignition coil (+ terminal = ground side).
Or, if a modern voltage control box has been fitted, check if the red box wire goes to ground (if so, it's wired +ve ground) or if the red wire connects into the main feed to the ignition switch, then it's -ve ground.