Help please, persistent EGS gear change fault.

Hello,

My C4 EGS shows service light and then no gear shift.
I bought a Lexia and found out the fault.
P1716: gear lever signal fault (short circuit to positive or circuit open)
P1750: steering wheel gear shift control signal fault (short circuit to positive or circuit open)

While clearing tbe faults, the service light goes off but it comes back immediately and the same fault codes appear again.

As far as I understand, the problem is with the wire(s) leading to gear shift mechanism. Can you please advise me how I can solve this problem?
How can I find which cable is related to these parts?

Thanks.