Obviously this thread is a bit old, but I just chased a similar problem down in my '92 YJ. Perhaps this will help someone, just in case it wasn't the grounding demon.
My heater fan went out, my wipers would work only on "Mist" but then failed altogether. The real pain came when the Jeep suddenly refused to start. It turned over strongly but would not fire. I had no power to the ASD relay coil or to the fuel pump relay coil. It turned out to be the ignition switch, which controls power to all three of these functions. As these vehicles age the grease dries up and parts wear. Inside the lock cylinder for the ignition this can result in a "lazy" return from the "Start" position, leaving a high-resistance condition between two or more of the ignition switch contacts. The heat causes the solder to melt and the contacts to arc and carbonize. Since nearly all sub-systems are controlled by the ignition switch it can cause demons in any of those electrical systems. Your fuses will all be good and you will spend a great deal of time hunting this down. Try wiggling the key cylinder and checking out how it rolls back from Start to On. If it duplicates or cures the "on again, off again" problem you will have your answer. If not, then you have ruled it out. There is an excellent posting on this forum by Opihi59 regarding the removal and replacement of the switch elsewhere in this YJ technical forum. If you do replace the ignition switch be sure to service the lock cylinder to prevent another failure.
So many people, believing so many absolute, but conflicting truths, cannot possibly all be right.