Neutral safety switch is a possibility. The next time it does it, try shifting to Neutral if you're in Park (or vice versa). That will frequently reveal a NSS that is starting to go bad. Sometimes a good NSS won't get triggered properly if the linkages are out of adjustment, so this is something else you can check.

You could also have a bad starter or a bad ignition switch, but look at the NSS first.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.