I just wanted to let folks know that I am finally in the process of installing the factory Ext Idle switch.
Instead of splicing the orange wire from the Ext Idle switch in the the orange wire on the fog light pigtail I did this.
I discovered in my '00 XJ that fuse #6, has a 5 amp fuse in it, runs all the little dashboard lights including the illumination of the symbols on switches.
You get 12 volts when the dimmer is at full brightness and a little less then 6 volts when the dimmer is turned all the way down.
So I put a fuse tap in there, had to turn it upside down cause of the relays on the left, and put 2 5 amp fuses in the fuse tap.
Wired that directly to the orange wire on the Ext Idle pigtail. Testing it looks like one bulb for symbol illumination in a switch has a draw of .12 amps.