Maybe this is unique?
Issue: My XJ (2wd, I6, 4.o L) will not start sometimes. There is no pattern to this, but it comes at very inopportune times. I turn the ignition switch, there is lights on the instrument panel but it wont start. When I bought it I used to unplug one battery cable, the red one wiggle it put it back tight and the Jeep would start....then this started not working and I just had to wait 15-30 up to an hour and then the Jeep would start. Since this was annoying and no one could tell me why it was doing this a mechanic friend in my church put a by-pass switch and whenever the regular ignition switch would not work I just push the button and it did. From time to time I would check the by-pass button to see if it still worked and it did except recently, tried to see if it worked and it didn't, been dreading the "no start for a while" symptom and yesterday it did it. While at Lowes picking some dirt for my house when I went to start it after the sale it didn't' start. Unplugged the battery (I had to go buy an adjustable wrench) but it didn't do the trick. Moved all the cables, shifted the gears but nothing...called a tow truck and 10 minutes before it got to where I was the Jeep started....This is so frustrating. My original mechanic couldn't tell why, he changed the ignition switch but a few months later , the XJ started doing this again...
I remembered trying to get some advise online and there is a definitely an issue with several years of the XJ and I couldn't find the exact cause of this despite some owners changing the switch (like I did) , the started, solenoids, battery, battery cables, started electric connections etc., etc.,...
That's when I found this other younger mechanic and he installed the by-pass, switch that worked until recently.
Now the only change I made (well I lost my new mechanic and had to go to my old one) , was that he exchanged my speedometer and instruments panel because my speedometer broke. I thought he might have inadvertyingly disconnected something so I went there my self and found:
1-The by-pass switch cable wont turn the Jeep when I short them (no spark, no nothing)
2-The switch is connected to a conector and it has a cable going to a red fuse plug (I guess power).
3- I have found several electrical plugs that don't connect to anything, the plug connections that would connect to them are missing (attached pictures)

So the by-pass switch is not working, how can I test it or buy a good one and connect it so it will work as before?

Any help will be greatly appreciated, since now I am afraid

By-pass switch and connector to the left of my hand-red wire connect to fuse box

Switch and conector-that has a red cable to a fuse plug.

Plug that doesn't connect to anything

It looks like a long fuse could have been used there.

Plug to no-where by the right light , on engine compartment.

Another two connectors to no-where on the engine (passenger side-front)
to ride the thing , because there is no telling when the thing will decide not to start again!!!

Thanks

 

Bypass all the factory wiring by connecting the switch directly to the solenoid on the Starter. Battery + -> fuse -> switch -> starter solenoid.

 

How do I do that, where is the starter solenoid?
Thanks
U21

 

On the starter. There's a large and a small wire. Replace the small wire with the wire coming from the switch.

 

Found the issue, a blown 15 amp fuse where the switch gets its power...but the new one blew as well after several starts...!

 

Problems with the crankshaft position sensor can also cause intermittent starting/running