Well, after soldering up the new harness, I got ready to install the radio this morning, but had a few checks to make before I went ahead and screwed it into the dashboard.
But let me back up and fill you in on what happened.
A month or so ago I went to a Hagerty Driver's Club event at the Scuderia Rampante in Erie, Colorado. The morning was cold, and the car radio was being really wonky about playing anything from the USB stick, and when I pulled the stick out of the socket, the radio reset, and then shut down ( ! ), causing me to have to pull off the road and try to get it going again. It finally turned on, but just sat there mute, so I sighed and continued on my trip. Sometime later it finished booting up, and started to work normally. Then the day we went to DIA to pick up my wife's friend, I started the car, and NO radio. Nothing.
Checked all the fuses, pulled the unit from the dash and reseated all the connectors and nada. So I coughed up the $$ for a demo unit that was a floor display at a stereo place. And of course, none of the connectors are the same, so down to the basement to make things match up. I also corrected some (*GASP!*) wiring and installation errors that I'd made during the original installation. I was bypassing the OEM 80W/channel amplifier, and I had a couple of speaker wires crossed up, so the new harness has been triple checked.
Last night I got out a power supply, and connected the old radio and the new radio to see if I could power them up. The new radio was very poorly packed, and I had doubts if it survived the trip, so I wanted to check it out. I connected the old radio first, and damn....it powered up just fine! Must be a problem with the car, then. The radio had the blinking 'standby' light before, indicating it was getting "12 Volts, Always On" which retains the memory, but was 'dead' when you tried to power it up. The signs pointed to either a bad fuse (there are two for the radio), a bad connection, or a bad wire. The new radio also powered up just fine and checked out, so at least I had two known, "good" radios.
This morning I checked all the fuses again, going so far as to remove them, visually inspect them, and continuity check them with my Ohmmeter. All were fine. So I shot the dice, and continued with the installation. Then I disconnected the battery and waited the prerequisite 15 minutes for the "System Capacitor" to discharge, and took the airbag off the steering wheel. I had to do this to replace the two back-of-wheel switches that control the radio, one of which failed a couple of years ago. It would only tune the radio going down in frequency, instead of tuning both ways, but it worked so I let it slide. When I bought the replacement switch for the left side (tuning control) I also bought one for the right side (volume up/down), so since I had it apart, I replaced both of them.
Then I neatened up the bundle of wires on the back of the new radio, and installed it in the dash. Reconnected the battery, and wonder of wonders, it worked! At this point all I can think of is that disconnecting the battery for a couple of hours reset something in a Power Control Module somewhere, or perhaps just pulling and reinserting the fuses did it. All the fuses were in physically excellent condition, and had silicone grease on the contact blades. The Jeep forums have mentioned disconnecting the battery to cure a variety of ills in the WK series of Grand Cherokees, with great success, so maybe that was it.
So it's a mystery for now, but it works, and I have a radio and navigation system again.
AND a nice, clean, used Kenwood DNX771HD to put on eBay.....