When red plug is inserted radio goes into transmit

Using the USDx radio. When I plug in the red plug into the mic the radio goes into transmit. If nothing is connected to the other end of the plug and red plug is inserted into mic the radio goes into transmit. If I connect the mic normally it works as it should. Is this a bad cable? The computer receives the signal normally from the speaker jack and the waterfall looks as it should if I leave the red plug disconnected.

Are you using a radio certified by Manuel DL2MAN? I am having success with Digirig and 40m digital modes with a radio certified by him.

73 Constrainted