I am 100% sure that this used to work, but having problems now.
My Flier ESC’s do not have 5 volt out, so I used to have an extra battery to power the Maytech receiver.
For some reason I’m not able to get this to work anymore 
When I use an “old” BEC that does supply 5 volts all is working fine.
I think that I used to have the external 5 volt on the BATT+ and the MOT connector (see image below)
Anyone here who can confirm that this is the correct way?
Never mind… I remembered that I used to use a Y cable over the GND / 5V. This was running to the external 5 volt.
Got it all working again.
Would you have a link to that manual you’ve taken the pict from ?
I got the picture from here.
The manual (V2) can be found here:
https://www.mhz-watercraft.com/media/pdf/ca/97/ba/Maytech-MTSKR1905WF-Manual-V2-0.pdf
I tapped power off the ESC (Fliers 400A) and ran a castle creation BEC and hooked up the Maytech V2 remote. We haven’t had any issues with this setup. The only thing that failed on my setup is the Fliers ESC.
I’m now doing the same.
I’ve got a small BEC attached to the positive and negative of the Flier.
The BEC is powering the receiver.
Last week one of my Flier ESC’s would not arm it’s motor.
I contacted Cathy from Flier and told here I was sad cause the ESC was broken.
Accessing the Flier was still possible (with the USB cable).
Cathy told me to reset the ESC to default and try again.
I did, and guess what. The ESC worked again… Pffffff. I was happy again 
My Fliers ESC has issues also. I tried resetting and charging the firmware with no luck. I have a new esc on the way. My esc made my motor just to sputter, and caused the motor to heat up really hot after a few minutes.
When turning the motor by hand (disconnected from the ESC) does it feel smooth?
The motor is fine, at least at the moment. I did pull the rear cover off to inspect it, and add more corrosion x. I then tested it with a friends ESC and it works fine.