Problems on throttle and motors

[tonylai]

I'm using one throttle to active two controllers which control two hub motors that are support by two independent batteries but common ground.
There both has a switch between battery and controller.
The wiring is like: (sorry for the ugly drawing)


My problem is when I turn on the switch of Battery 2, which powers the Controller 2, the Motor 2 just start to speed up without spinning the throttle.
The problem won't happened if I turn on the switch of Battery 1.
Can anyone tell me why?

 

[vfr400]

The throttle signal works between 1.2v (zero throttle) and 3.8v (ma throttle). What voltage do you have on that wire when you switch on? Are the 5v and throttle ground remaining disconnected on that controller?

You get that sort of problem when you don't have a common ground. Are you sure that you have continuity between the two battery black wires?