Thanks for providing your component information. Always helpful to see what one is working on.
Caution: With the upcoming suggestions, always keep in mind to keep the positive
high voltage battery pack voltage
(Yellow wire) separate from the
low voltage 5vdc regulated supply (Red wire) and output (Green wire) of the throttle's hall sensor. The ground of the hall sensor and the volt meter are shared. (Black wire)
Two possibilities come to mind. A "passive" type control. Or a more "total" control wiring. Both would use the volt meter on your new throttle.
Passive: I would re-wire the throttle internally so that the high voltage positive wiring only goes to the voltage meter
directly, having removed it from having anything to do with the key switch. Then use the key switch to make or break the 5vdc incoming voltage supply (Red wire) to the hall sensor.
This would bring on the voltage meter immediately after the battery is plugged in. And only allow operational control of the throttle
when the key is in the "on" position.
Pros: No extra parts or extra wire runs needed.
Cons: Internal throttle wiring changes which may require soldering. No disabling of power to controller with possible parasitic drain on battery if left plugged in?
A more total approach would be to use a
control relay connected into in the battery to controller wiring. With it being energized by the key switch @ battery voltage.
A solid state relay is what I would recommend.
Your systems voltage and controller's maximum current use would be necessary to size.
This is the one I use on my system. But I also use the provided push button lighted switch. See it being used in my build log, accessed thru the link in my signature below.
https://lunacycle.com/remote-on-off-solid-state-switch/
You would be able to use a SSR like this, but would have to run an extra wire to your throttle. (6 wire cable)
I use both methods on my system.
I tried to describe a couple possibilities that may be of interest to you best I could. If I've not been perfectly clear, you have questions or other ideas and need more information, please let me know.