After much figuring and fixing with the wires for the dash indicator pilot lights I finally had to rig them directly off the wires headed out to left and right sides of car and by-pass original wires that no longer worked.

After all packed back inside the dash I now find that my right hand indicator is good but my left hand one activates all the dash night lights as well. What might I have crossed, where to look and is there a common reason a feed from the indicator would start to spill to the dash night lights?

 

I think you crossed a wire destined for the 4-way hazard / emergency flashers. And that is just a wild guess, but based on my experiences with my 1984, the hazard switch is key in the lighting circuit of the XJ.

you might study the wiring diagram of a 420, which was made until 1969, the Series 1 XJ of 1968 has a lot in common with the 420 wiring.

 

Really hard to comment once creative wiring is play. One the later model XJs those turn dash lights have diodes in series to stop voltages gettinh where they arent wanted. If you spiced on the wrong side of the diode (hidden in harness) you may have triggered the very thing they are there to stop. Only a guess based on later series XJs.

 

I've recently bought myself a series 3.
Fog lights wouldn't work and then high beams, then indicators..........
In the stickys at the top is a link to the electrical diagrams.
Download it!
My fog lights and indicators now work and I'm gradually going to go over all the wiring and whatever doesn't work or match with the original diagram, gets removed and replaced. Going to change all my fuses to blades, but restoring everything else.
After all, it all worked when the vehicle prowled away from the factory and they do know their stuff.
I'm happy to pull things I don't understand to pieces. But jag released the sort of diagrams, with which, I could just about reproduce the entire vehicle from scratch.
Moral of this tale?
Always do what the maker did. Don't wire into another circuit, replace one if faulty.