Help needed 1987 420SE

I am posting this for a friend that works in the same garage as me. He serviced a 1987 420SE V8 after the service he road tested it and all was fine. When the customer came to collect it, it refused to start and was
found not to have a spark at the plugs. He has changed the ignition amplifier and checked the obvious but is still the same. Do these have any blink cods that can be accessed to help with finding the fault. Or is there a common fault that gives this problem..
Thanks In advance Ken.
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Does this car have some kind of alarm related spark killing device?
Just a thought...
Marty
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