This may have been talked about here before.
I ran into a No Start condition about a year ago.
Left my XJ ay his hous while fishing with him.
Returned from fishing,it starts and dies 3 seconds later.
Symptoms:
Motor cranks
No fuel
No spark
No guages
Nothing.
After some searching the web I had a No Buss condition.
Problem:Crank Sensor shorted to ground and sent electrical into
No Buss condition.
Quick check-Unplug crank sensor and guages come back.
Replaced crank sensor-Presto back on the road.....the next day.