A small update.
I decided to connect diagnostics first and found RFH Error.
MaxiECU Had: B1035-01 : Button Pressed - General Electric Failure
MultiECUScan Had: B1035-01 : External handle input for Passive Entry - General Electrical Failure
Interestingly the Fiat eLearn diagnostics have: Button Pressed - General Electrical Failure B1035-01
So we have two different descriptions of the problem. Now the door handle sensor connect to the RFH as does the Start/Stop button.
I also found that the error once cleared reappears when the Start/Stop button is pressed.
I gained access to the RFH module and noticed small drops of water on one of the seams facing the rear. The module also slopes backward to rear and right end down.
The cables themselves felt dry.
I need to inspect in greater detail tomorrow (weather permitting) before removing the module and connectors. The purpose of doing this is to see where the water is coming in. Based on what I have seen so far I think it may be from where the boot seal goes round the top of the hatch back/roof line to wrap down the C post upper wing lip. Right in that top left corner the roof and upper C post join with basically on overlap this creating a ridge. Also as it is on the bend then the usual rubber seal profile will probably be bending/bulging a little.
If what I suspect is the water ingress method is correct then I think the fix will be fairly simple.
1) create a shield / shroud over the top of the RFH module
2) lift the tailgate hate rubber seal, clean any rubbish out, reform the bend area and then put back with loads of Waxoil
Fingers crossed the module / connectors when cleaned will be be back up and running OK.
Will keep you all posted.
Nick