Hello folks,
Why is my esc doesn't work when I remove the red wire from the receiver plug to the receiver?

I use a separate receiver battery pack to power my steering servo and receiver, so naturally I should disable the esc internal bec so the receiver pack and bec doesn't coincide with each other. I disable the bec from the esc by removing the red wire from the receiver plug. This leave the receiver plug with only the signal and the ground wire. In general the signal wire only needs the ground wire to work properly.
When I plug the receiver battery pack to the receiver the servo and receiver work properly in response to the transmitter, the lights on the esc respond properly to the transmitter, like when I pull the throttle trigger to advance the throttle, the lights on the esc ramp up accordingly. But the motor doesn't run. WHY?
On my helicopters, I just simply remove the red wire from the receiver plug when I wanted to run an external receiver pack and the esc and motor work the way it should.

Now when I plug back in the red wire on the esc receiver plug and use it with the external receiver battery pack the esc and motor work properly again. However, there is another issue that I notice. The esc will respond to the transmitter command and engage the motor from the power of the receiver pack, without the main battery pack plug in.

Tekin rs pro
Lrp x12 17.5
1s lipo

Thanks