All of the plastic behind the ignition switch has crumbled! Is there a work around that would allow an on-off switch with a push button starter? I have tried a number of new and used vendors and the parts do not exist. The car sits here unable to be started! About ready to sell it for scrap!

 

https://www.jagbits.com/product/DAC1422.html

This may be part you are referring to.
Rgds
David

 

yes there might be a workaround and the parts do exist from Jaguar cars.
The 1960's Small Saloons before the XJ had a "Ignition ON / OFF" switch with Key, and then you press a push button to crank the engine. Can it be adapted to the XJ ? I have no clue.

I have both parts in my classic S type parts website that you can look at
https://classicstypeparts.webstarts.com

 

Looks like you have a Series II, Yes?

I think a switch from a Series III will work

More possible sources:

https://www.ebay.com/itm/155453242549

https://www.terrysjag.com/product/DAC1422.html


Also try David (great guy) at :

https://everydayxj.com/

Cheers
DD