Found in a folder the manual for this decoder. The cause ot the ticking was CV60, the BEMF enable / disable bit variable. This CV also allows to set the error reporting for any short detected by the decoder in CV30.
Which I read and saw that the motor and a light had triggered a short.

So I reset CV30 to all bits=0

I left CV60 with bit1=0, no BEMF, and bit2=1 for error detection.

The decoder manages to drive the motor.
I read all the available CVs and set them properly, IMO.

A curious thing, if I insert a CV higher than the allowedd maximum value it is entered without generating an error, I believe that they didn't have much error control in 1996 when this decoder was made.

I will have to try with another decoder to see if BEMF behaves the same way or not.