Z1r battery gauge

missionkz wrote: ... then use Ohm's Law.

Yup, it's true. But my guess is that the shunt wire is something like 18 awg, so at 1300mm the shunt would have about 0.03 ohm resistance. That would require 33 amps of current to register 1 volt across the shunt, which is kind of a lot of current. So this method might be a bit tricky in this case

Back to the front of this thread.... there is no excuse for the meter not working correctly and detecting current flow, forward and backwards.....unless it is junk and needs 30A-40A to show full deflection, or it is broken.
What you need to do is find out what tiny DC voltage puts the needle at max deflection.
Then calibrate the shunt to show that with a known current/load.
I have done this with an 8-10 gauge piece of copper wire as a shunt and a dremel tool to thin it down until it read the same current as my digital did.... A pain in the butt if you ask me
There used to be lots of info on how to calibrate and or determine uA of a meter's movement in the ham radio digs.

Personally, I would just get a different meter/movement to install it in there.

missionkz wrote: Personally, I would just get a different meter/movement to install it in there.

This is clearly the correct answer.

But now I am curious how the factory engineers intended it to work.

To show what you already know when the lights go dim and you smell burning plastic? :ohmy: Just joking.
I had a AMP meter on my bike years ago. I drilled a hole in the side cover for it. I ruined a good side cover for something that was worthless. I put in a volt meter and could tell if my battery was charging and how the system was doing.
Steve