Hello all from Aus!

Im currently having an issue with my 86 FC. Recently (bout 3 weeks ago) my cars ecu (Microtech MTX8) and headunit turned off while driving, in turn shutting the motor off. Lights, p/windows all worked.
I turned the key off and pulled it out, tried again, the car kicked over and then died.. ecu and headunit off, but again, lights all worked.

Now, heres the tricky part.. my headunit is on ACC and my ecu is on IGN. They use DIFFERENT ground points
An auto elec checked it today, and he couldnt get the car to fail electrically. He said my grounds were all good for my headunit and ecu. Unfortunately, he didnt want to go further as the car wiring is an absolute mess, apparently.. (previous owner )
.. so now im stuck with a car which has the most random problem that not even an auto elec has a clue on..

A few people have mentioned the ignition barrel - which is the only problem I can see aswell.

Has anybody ever had an issue like this?! Was it something else? Anything anyone can reccomend me.. any ideas?! I really want it fixed now!