Update: Wound up buying the XJ Sunday morning and had to leave for NH Sunday night (made a pit stop in CT to watch the SuperBowl).
I had a hunch that the problem may have been a blown #11 fuse on panel located on the interior fuse block. I pulled that fuse on my '01 XJ and was able to replicate 2 of the three major symptoms I was observing with the '98 XJ, which was no voltmeter or fuel gauge and no power to the fuel pump. Couldn't replicate the P1694 code - my code reader just kept saying it couldn't connect to my computer once I pulled the fuse.
So, I arrived on Sunday only to find all of the fuses were fine, but I swapped the #11 fuse out for good measure - still nothing. Decided to get the truck anyway since the body is in real good shape and the thing only has 71K miles on it. Also has a brand new windshield, brakes, shocks, and battery. I think the combined cost of all of those parts are probably more than I wound up paying for it. I had roughly one hour to work on it before I had to leave for NH, but I'll summarize what I was able to get done.
1. Unplugging the crank position sensor DOES NOT give me my gauges back. I tested the resistance between pins A and B, B and C, and A and C. Each test gave a reader of anywhere between 1000-1250 ohms. According to the link that was posted earlier in this thread, there should be NO ohm reading at all and it should be a completely open circuit on all of the pins? Am I understanding that correctly?
2. I swapped relays around like they were playing musical chairs. Even took my known-good relays from my '01XJ and swapped them in - no changes.
3. ALL fuses, both on the interior panel and in the underhood power distribution center are GOOD.
4. Although I knew this was likely a bad idea, I did it anyway as I was desperate and needed to figure out an answer quickly. I swapped my '01 ECU into the '98. They should be different in a lot of respects since the '01 has FOUR O2 sensors and coilpack ignition. Naturally, when the '01 ECU was swapped in, it threw codes for non-existant O2 sensors (duh) and some other emissions control thing. The P1694 code also came back, but here's the kicker - my volt meter and fuel gauge came back! Still nothing from the fuel pump and I didn't have time to check if I was getting voltage back to it as it could be bad and not kicking on at all. What seems odd is I sometimes get a little drip coming from the fuel bleeder valve if I push it open after many attempts at trying to get the thing started.
So, from my very brief testing, it would seem to me the ECU may be bad, but I'm not convinced and that's a lot of money to spend without really knowing. I may trade XJs with my girlfriend and get the '99 since they should have more similar ECUs. Also, while I'm thinking of it, the current ECU in the '98 also does something kind of silly. When the P1694 code is read on the scanner and you try to erase it, it won't let you because it says the engine is running! Well, that's obviously not the case since I can't get the darn engine to run! If you hit retry on the scanner, it will then erase the code no problem.
Anyone have any other suggestions? Obviously, I need to test for power at the fuel pump - that'll be my first test when I get back, but if there is anything else or if any of my testing notes from above seem odd, let me know!