Not even a click.
Where should I start looking? I am not overly mechanical but have a volt meter and willing to get hands dirty.
Starter gone? Is there an easy way to apply current with booster cables and second battery? Something else in electrical system?
Any advice appreciated. Would like to try to at least diagnose the problem before I tow it to a garage.
Viking1
What year and model?
Cheers
DD
Hi. In order of failure, battery is first higher probability, in second starter which is in contact with ground (solenoĂŻd) and cut electrical feed, in third anti-theft contact out of use (more rare) . So I suggest first to try a battery in good health.
1987 Van De Plas
Can swap the battery out. Tried it while boosted (charger connected and in “start” boost mode) and nothing so kind of ruled out the battery. Could be that it is shot and is the problem.
This was written with the Series III XJ6 in mind…but the basics apply to your V12 car as well
https://www.jag-lovers.org/xjlovers/xjfaq/nocrank.htm
To clarify “nothing”…
Are you saying that none of the dashboard warning lights come on when you turn the key? Interior lights inoperative?
With a booster battery in use these things should work even if the starter doesn’t. If not, you have some poor connections somewhere. Battery cables, grounds, perhaps the “+” voltage junction posts on the firewall.
Cheers
DD
Car has interior lights, dashboard and power warning lights etc. just nothing happens when turn key to start. Sorry, should have been clearer.
Viking1
Thanks for the link. Will investigate further next week. Feel like the part on the firewall may be involved because previous owner had wired some additional electronics there and seems to be a lot of tape there that doesn’t belong.
That’s always worrisome…
Start with the basics:
Battery voltage
Inertia switch
Ignition switch contacts
Starter relay
Starter connections
Starter and relay at the starter
Aristide is right, you must proceed step-by-step. It seems there’s a cut in feed, bad or not ground somewhere,…Jaguar manual could be helpfull in this work.
please test (ignition on) for each part of the process + and - hubs with a multimeter. On relays, test + circuit before and after ignition. If good, power enter buy a terminal and go through another to feed part.
Move the gearstick from park to neutral and then back to park again. There is an inhibitor switch that prevents you starting in gear.
viking1,
What is the history of your car? Did it start and run properly for you and then just randomly failed to start one day? Or did you acquire a non-running car and you are trying to get it running for the first time?
Some of the more difficult problems that I had to solve in my Jaguars over the past 23 years were due to modifications made by prior owners or their shops. There is no limit to their creativity and they never document anything. 
If you acquired a non-running car and you are trying to get it running for the first time, it is possible that a prior owner had some kind of aftermarket anti-theft device installed. If that is what happened, you will have to remove all of that stuff and get your car back to production configuration before we can help you.
Your problem sounds like more of a car related problem instead of a V12 engine problem. You might get more help on the Jag-Lovers XJ list.
BTW, I have a Canadian market 1990 V12 Vanden Plas, which should be very much like your car.
Take a picture of the added electronics and post it in your reply. Maybe we can figure out what it is.
Paul Novak
Viking1,
In the V12 Series III saloons the fuel pump should normally come on for a few seconds and then go off automatically when you turn the ignition key to the “On” position. You may not hear this sitting in the drivers seat, but if you open the trunk and have someone standing by and listening near the level of the bumper they should hear the fuel pump turn on and go off automatically when the ignition key is turned to “On”.
I recommend that you do this simple test to see if your fuel pump comes on or not.
Paul