The inverter neg would go to the outer end too but only if you are using the ammeter to measure draws not charging inputs, with the one way meter.
I just tried to calibrate my ammeter part and the same little screwdriver that turned the voltage pot easily would not turn the ammeter pot so I pushed harder and the pot screw head came off!!! Drat, very flimsy. So now there is nothing to grab onto to turn it and it is stuck. Also I must have done something because it was reading 3 amps (with 12 amps worth of lights on) and after I broke it, it read 234 amps. Phooey. So now I have a $12 voltmeter and don't need the shunt. I think the shunt will make a good buss bar for another job though.
Hope your meter project goes better than mine did! :)