Thanks for the suggestions. The body control unit, do you mean the one above the accelerator pedal? There was a lot of condensation under the dash when these problems started. But I have taking the control unit out and swapped it around with my other Fabia. Both control units gave the same result.
I've put a new battery in, the largest that would fit. Swapped alternators around, cleaned grounds, replaced negative terminal and replaced part of the dmf wire. The multimeter shows 12.6 v at battery with ignition off and 14.3 v running.
Would a global issue (voltage, wiring) create so many symptoms or could a simple sensor issue (abs, steering angle) overwhelm the system?
Thanks for the input!