There are two cables, one from the handle to the rear connected to the second cable that goes between both rear wheels.
My guess is that the rear shorter cable is gone. There is a loop in the differential housing that it runs through and that wears the cable.
I've changed it but I really dont remember how long time it took, maybe it was about an hour. The tricky part is to put the hardware at both ends of the cable in the right position inside the brake mechanism.
If you have never removed the lip at the edges inside the parking drum brake there could be a problem removing the rotors. Loosen the adjustment at the handle, behind the rear ashtray as much as possible.
If it is the longer front cable I don't know how to approach it.

Good luck
Mikael Larsson