THE INTERNATIONAL JAGUAR 'S'-TYPE REGISTER FORUM

And a tip to preserve the lock barrel, do not have a lot of keys on your key chain dangling from the lock. A while back Chevrolet had a recall on steering column ignition locks on certain cars as they could inadvertently get turned off while driving from too much weight dangling on the switch. Remote key fobs might have been part of the issue but switches were too sensitive.

With the key off there should only be the main live going to the switch which is the brown/white. The other two become live when the key is turned. One goes to the starter button and the other to the fuse terminal which powers all the electrical systems such as fuel pumps, lights and gauges.
I doubt that the conversion to Negative earth has altered the wiring on the back of the key as there is no need to change any of the polarity in this area.
The switch can become worn over time as can the key making a floppy connection. A bit of copper grease in the key hole might firm it up a bit. They are very easy to strip out and take to pieces. They do not cost a lot to replace if worn but you will then have a different key to the doors and ignition. The Keys are what are known as FS keys and on the barrel of the ignition switch there will be a number. This number is the key code for both the ignition and door key. If when you buy a new ignition barrel you quote this number the supplier might be able to match up the new barrel to your key code retaining the same key for ignition and locks. If it is the key that is worn then new keys can be bought from https://www.replacementkeys.co.uk/unionfs-series-keys-to-code.html?gclid=Cj0KCQjw8vqGBhC_ARIsADMSd1Asndli2VxJLMXgwXlrv9yHPs9hdSUfT3e5bpmhDS94K1qdUW35HL4aAuK4EALw_wcB You need to quote the FS code for the key which is on the original key or as described on the lock barrel.
There were very few FS key combinations, I think less than 1000 so every 1000th Jaguar coming off the production line had the same key combinations. FS keys were used on so many cars in the 1960s that thieves used to walk around with a bunch of FS keys on a ring and were guaranteed to have the right one to break into and steal your car in minutes.

Below are two photos of the ignition lock showing the barrel release hole and then a second of the barrel showing where the FS number can be seen.

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I was going down the road fine, then suddenly the engine shut off. Tapping the key switch allowed me to restart, so I think that is faulty. I bought the car after the negative ground conversion, so likely the wiring is non-standard.

The wiring diagram says there are three wires that attach to the switch - one white to the starter push, one white to a fuse terminal, and one brown/white from the control box (live). In my case, the live white goes to the left terminal, the starter push off the right, and a blue to the center.

I plan to disassemble to check the continuity of the switch, but there are three terminals on the back. Should I expect key "on" to activate both cold terminals? Or is there still one live terminal with key "off"?

Thanks to all
Euler