A thought occurred to me as I perused the first post here.
Approximately 34 to 35 years ago, I purchased a one-year-old Vauxhall sports vehicle. Initially, it operated exceptionally; but, after a year, attempts to start the vehicle from a warm engine sometimes yielded no response, including no sound when turning the key, if I recall correctly—it was attributed to one of the relays. I was fortunate to visit the main dealer, where the receptionist suggested I try a relay switch, a little oblong item. He provided one for testing, allowing me to return it if ineffective; it resolved the issue.
My vehicle was equipped with a petrol engine and electronic fuel injection.