Hi David,
Welcome to the forum. I am sorry to learn of your predicament, as resolution is not usually simple.
Action Plan.
1. If as is common, you do not have an emergency code card for the vehicle, take immediate action to obtain the emergency starting code from Fiat. This may take some time, and I would expect you to be required to prove vehicle ownership. If you are a member of AA or RAC, they may be able to assist in negotiations with Fiat.
You should be able to start the vehicle with the code, by following the procedure in the Fiat vehicle handbook. This starting procedure is protracted. (The emergency start procedure does work for diesels.)
2. Try disconnecting the starter battery for a few minutes.
3. There have been some posts (I can't remember where.) concerning possible bad connections at the code receiver multi pole connector. Try unplugging and replacing the connector, but disconnect battery negative while doing this.
4. Budget for a substantial bill.
5. Consider referring the problem to a Fiat Professional Garage (expensive), or possibly having units recoded or repaired by a specialist company.
6. If necessary revise your holiday plans.
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There have been several posts on MH forums concerning problems with MH electrics failing in similar circumstances, also I have seen mentions of the airbag system being vulnerable. It appears that the code receiver and/or ECU are similarly vulnerable. Not sure whether it is just memory (code) corruption, or component damage. It does appear that a slowly decaying voltage may be the cause.
Please see attached extracts from eLearn for some background knowledge.
Also please post updates to assist others.
