Ferrari 328 GTS, electrical failure over 3 days

I just got my 1986 328 out of the garage to have its UK MOT done before the summer. It started fine, I reversed it out of my garage and it was driven to the MOT garage. The garage called me to say that the engine dies intermittently and then every time they put it in reverse, but that pressing the reversing light switch by hand didn't cause the problem.

They then called to say that they disconnected the reversing light switch and it no longer cut out when being put into reverse.

They then called to say it had started to cut out intermittently at other times.

Finally, it has died entirely and no dashboard lights come on when the ignition is turned, although the engine will crank (I believe this is a direct connection from the ignition switch). With the ignition on we can't even get the window to go back up i.e. all the electrics appear to be non functioning.

The garage has looked at the fuse and relay board in the passenger area for anything obvious but nothing apparent was observed. They are not a Ferrari specialist garage.

I would welcome any thoughts from anyone who has experienced anything similar or what the right course of action might be to diagnose the fault.

 

Thanks, will give that a go.

 

The battery lives on a battery conditioner and cranks the engine very well indeed. Not checked voltages but seems fine on this basis.

 

So the garage removed the earth cable, cleaned it up and reattached it. Unfortunately it has not resolved the issue. Battery is strong and cranking engine well. Any other thoughts?

 

I would like to say thank you to those that offered valuable advice. In the ended my local garage and I admitted defeat and sent it to an electrical specialist. This is there final report I got back yesterday - seems like I had a catalogue of faults and really surprised it actually started from my garage in the first place.

Confirm good supply to ignition switch.
Confirm Immobiliser is not triggered by remote fob.
Temporarily bypass immobiliser for testing purposes.
Testing centred around fuse box. The ignition relay appeared to be incorrect as the pins and fusebox contacts did not match.
The fusebox was removed and dismantled. A contact for the relay was found to have broken off completely. The contact was repaired and refitted. One other contact was failing in a similar way and was also repaired. One of the main supply pins was suffering dry joints so these were repaired also.
When tested, it was found that the car could be started.
The alternator warning light was found to not be working. The bulb and associated wiring in the instrument area was checked and found good. The supply was checked and found to be present. The alternator was confirmed to work, delivering 13.9V.
When tested, it was found that the intermittent cranking problem had returned. It was found that when the car would not crank the alternator warning light came on. It was felt that the problem related to loss of power to the starter motor and alternator. The car was lifted, and the engine wiring was checked. A single way Anderson plug was found under a cover which was extremely corroded. A loose connector was found which was the colour of the warning light signal.
The Anderson connector was dismantled and cleaned. The main connection to the starter motor was also removed and cleaned. Another wire was found on the starter solenoid which did not belong. This wire and the spare wire were connected.
The engine now cranked reliably and the alternator warning light now worked.