Well, I finally did it. After years of reading, over-analyzing, feeling like every solution I found only got me half of what I wanted, and good instructions disappearing due to photobucket being a garbage company, I now have an e-fan that I can turn on when wanted with a switch, and will run a timer post shutdown.
I followed the directions in this thread.
https://www.cherokeeforum.com/f51/right-way-install-manual-switch-your-e-fan-212243/
I then attempted to use the time delay relay mentioned here as a way to not have to do a separate timer:
https://www.cherokeetalk.com/forum/f64/xj-heat-soak-fix-simple-inexpensive-fan-off-time-delay-69801/
Unfortunately the diodes in the time delay relay prevented it from working backwards like the CF thread mentioned. So I swapped it for a normal 5 pin relay and boom, had a fan I could turn on with a switch when needed that would still operate normally without a CEL.
So the next step was a timer. I know the ELK timer is the one most folks use, and I had one, but the ELK seems to work best with a momentary switch. I wanted to use a carling rocker to match the other switches in my panel and be able to have one switch that ran both the timing operation and manual operation. I found this timer on amazon:
https://www.amazon.com/DROK-Automot...ds=12v+off+delay+timer&qid=1578338157&sr=8-11
Mode P-4 on this timer was exactly what I wanted:
P-4: If there is signal triggering, the relay connects and keeps connecting. When the signal disappears, timing starts. When the time is over, the relay disconnects.
So now I can turn the fan on with the switch, and its on. When I turn the switch off, a 4 minute timer starts and runs the fan off battery power.
The one thing I don't like about the timer is the digital display is always on when receiving 12v power. The manufacturer claims only a 20ma draw in standby with the display on, but I'd still rather it be off completely. Looking at another timer I've found that is almost identical but has the option for a low power mode with the display off.
There you have it. I was terrified of this mod for years due to the wiring, CEL issues, etc. It took me about 2 hours to do all-in. If I had had all the right parts at first it would have been one afternoon.