84 Rolls Silver Spirit - Total black out. Need Advice on tracing from battery

[Dennis in CT]

So I have a very well maintained 84 Rolls Silver Spirt that is a Sunday every once in a while driver. Took it out for a drive the other day - parked it - came back an hour later and turned key - no power. Nothing.  Fortunately it was parked next to my shop - tested battery - totally fine. Cleaned terminals, still nothing. Have the factory service manuals, but they are rather useless really and I need to know what I should be looking for between the battery (in the trunk) and ignition. I literally have NO power. Not even a dome light. Checked fuses, relays, even pulled the dash apart and pulled out the ignition switch, which appears fine. Any Rolls folks out or anyone else have a thought of where to look next? My only English car. Thanks