This informations has been found with a genuine TRS-80 cable and a multimeter.
|4||Audio In||Loading from tape|
|5||Audio Out||Saving to tape|
The TRS-80 have relay contacts for motor control (2.25mm jack). Audio in and out are 3.5mm mono jack. Pin 6 and 7 are not connected on that original cable. Pin 8 is simply non existant.