Question 1: If we disconnect the Rx, the light ring is still on. So we have to disconnect also the accu (from the ballancer connector of the 4s Lipo) for supplying the lightring. Is that normal?
Answer: The controllers NF-Jet can work in two modes. Either as controlled by Rx (when the Rx cable in connected to a receiver) or as non-controlled (when the Rx cable in not connected to a receiver).
In controlled mode the intensity of the flame follows the power of the engine. In non-controlled mode the light intensity is 100% (full gas).
When you disconnect the Rx cable the Jet controller switches to the non-controlled mode and sets light intensity at 100%. So if you would like to only switch the light on and off ( in non-controlled mode), the simpliest way is to disconnect the power as you mentionned.
Question 2: We use your Jet controller in the control-mode. It works very well. But if we switch-off the Receiver the light is still on! Is that normal?
Answer: If You switch the receiver OFF, it is the same as if you disconnect the Rx cable. The Jet controller detects mode "no receiver" and starts work in non-controlled mode so it sets the light intensity at 100%. The simpliest way how to solve this problem, is to use a "two poles" switch and switch the lights at the same time as receiver.
Question 3: There is a "Y" cable diverging on the board of Jet2 controller. Is this with or without an amplifier? I ask this because of a warning by Spectrum RC.
Answer: Yes, each output of the onboard Y diverging has the amplifier. But attention : the "+"(red) and "GND"(brown) wires are diverged too and pass from the receiwer through the controller to output pins. So if you decide to use this diverging and engine controlers hawing their own BECs to power the red wire you have to ensure that only one BEC will power the red wire ( doesnt matter if it will be Rx´s or engine controler´s BEC). Do not connect unused red wires to the Jet2 outputs otherwise it could cause mischief.