Well it has been some time since I visited you all. Cheers. I decided to fix a couple old issues on my 1991 XJS that bother me like a dim dash and old wood. So I changed out instrumentation to LED’s from superbrightled’s. Very exciting to see that dash look so spiffy. Well in true Jag form, the car now won’t start. I don’t have the instrument panel all the way in but it’s plugged in fine. Car turns over but no ignition. Maybe I shorted something? I will pull coil wires etc to check spark, but anyone got anything?
You didn’t accidentally trip the inertia switch did you.
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Maybe a bad connection to ignition switch got bumped?
And what do you mean it won’t start? Does engine turn but no start? Or does turning the ignition key do nothing at all?
Got the goofy thing started. It was turning before fine it just wouldn’t start. Still not sure what it was. I checked the coils both working great. Then I took a look at all the fuses. Jiggled a few wires under the dash. Boom started up. Well hopefully whatever it was that was loose stays tight. I don’t remember and inertia switch. Need to look that up.
That sounds like an ignition switch problem to me? Or the wire from ignition switch that supplies + voltage to the coil sounds intermittent?
While it’s idling, try jiggling the key in the ignition (wiggle as much as you can without turning key to another position) and see if it stalls. That would be a bad switch.
While it’s idling, try jiggling the wires under the dash and see if it stalls. That would be a bad connection.
Good advice there. But, you really should try to “fix” the problem or it will re-appear at the worst possible time.
Phillip
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Yep thought of that happening at a bad time now that I know something was loose. Will do some jiggle tests while running. Thanks guys will report back. 
I’ve had ignition switches go out on me on other cars that are 20+ years old, pretty common. Turning that key a million times, the contacts within the switch just get worn out.
Also, I know nothing of how the + wire is connected to the ignition switch on the XJS. Maybe someone else can chime in, perhaps that connection is a common one to get corroded? Perhaps a simple resoldering is in order (with battery disconnected!)
And if you can get a no-start condition again, check the + side of the coil with the ignition on. No 12+ volts = key ignition problem.
Got it. Remember this car was working perfect until I pulled out the dash instrumentation this week and changed bulbs. Likely jiggled something loose and back again.
True, hopefully it’s just a connection.
The “mechanics” of the ignition switch in my 89 failed a couple of years ago at about 50K miles. It would not stay in “run”, it would spring back to “on”. I had to drive it home holding it in “run”. Couple hours to swap to a new switch. The breakway bolt that holds it in place was a bit of a hassle as I recall, but I got it figured.
Hi Guys,
Well today is my birthday. Happened to get all my refinished dash wood in from Saul / British Autowood. Which is absolutely beautiful by the way. Just gorgeous.
So was excited today to get the instrumentation in and replace the wood and new ski slope with cupholders. Remember, somehow with some poking around under the dash or in fuse boxes and or with the instrument panel being pulled in and out I had gotten the car running a couple weeks ago. So figured I would do some jiggle tests while its running as you suggested so it doesn’t strand me before I reinstall the panel. (my wife said whats wrong-to which I replied a jaguar complicated like a woman and I do not know which wires we may have here causing a problem)
Well it will not start. Coils are both firing well. Tried a spare new key I have. BTW-never have had any issues with this until removing instrument panel. Car only has 68k. Just nuts. So now I am jiggling wires and harnesses while trying to start it but nothing. BTW-never have had any issues with this until removing instrument panel. Car only has 68k. ??? Someone mentioned a motion sensor switch or something?
Oh and one more clarification. The starter is turning. And again the coils are sparking…
SOLVED. Baxtor you had mentioned inertia switch. I realized that I was in fact not hearing the fuel pump running with the key was turned on. So I pulled off the cover of the wiring above the batter in the trunk. The main harness / plug assembly was loose. The day it stopped running I had a mobile paint outfit come to the house to repaint the end of the deck lid. The sanding and buffers and all must have been just enough to unplug what was already a loose harness. Just nuts.
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Awesome! Glad you figured it out!