Slartibartfast

I know that harness comes into the body on the upper left (looking from the outside) of the jamb for the hatch, but I'm not sure where it runs from there. I would use the manual to see what the color of that wire is (there's a list of color codes in the "how to read wiring diagrams" bit), see where the harness it goes into runs, then get into it at its closes point to the alarm and look for that wire. If the diagrams in the manual aren't helpful, you could unscrew the plastic trim from inside the rear hatch and see what the wire looks like where it attaches to the actuator--it should be the same in the harness.

Hit around the edge of the door with my fist to break the ice so I could open it. Also discovered that the little sliding nuts in the roof rack bars have plastic springy bits underneath them, and that if you thread in a stud and thump it to break the ice, the springy bits go all to pieces. Oh well, at least I didn't snap the door handle this time.

Good to hear! The remaining washboard effect has to be something to do with the front drivetrain, if it only does it with the hubs locked. Looks like CVs are ruled out, so I would have a look at the U joints in the front drive shaft. Looking back over the thread, you might also want to pick up an idler arm brace if you haven't yet, looks like it's the last weak link in the front end.

Good to hear it's up and running! I had issues with the cargo light on mine and ended up disconnecting the switch for it in the hatch latch. It's kind of a lousy design and the rubber bit for it was worn out. I re-routed its lead to the switch for the tire carrier idiot light (had to add a diode in line or it would light up the tire carrier light with the key out--that was a fun one to track down) and it's worked great since.

Aired down the snow tires and dragged my mom's Honda up the driveway through six inches of wet nasty slush. The weather report said we were getting rain all today... we got the white fluffy kind of rain that breaks trees.

The '89 is TBI, so it's just got the two injectors. All I can think of is a wiring fault between the ECU and the #2 injector. You could probably figure out which wire it is on the ECU plug and test from there to the injector plug.

I don't think a gutted cat would cause the motor to run rich.

Read a couple Youtube comments sections and you'll find idiots who think there is one already.

These ancient people had advanced petrochemical technologies... but had not yet mastered stoichiometry. Actually, mine's the same way. I keep meaning to give the coolant temp sensor a proper check.

Why not swap in a set of 4WD upper control arms, if the 2WD arms are that troublesome?

It sounds electrical to me, like something's loose or a sensor is on its way out. Hopefully the computer will tell you what's up. The tach acting up makes me think it might be the camshaft position sensor, but it's not a symptom I've heard of before.

Have you replaced the fuel filter?

Here's the thread:

A shorted cigarette lighter should take out the room lamp fuse IIRC, which would take the lights/clock/stereo with it. I would take another look at the room lamp fuse, maybe switch it for another of the same size just to be sure. I've read that they can crack and not work but still look fine. If it's not the fuse, then all I can figure is that another connection on that circuit was weaker than the fuse and blew instead.

Flares are not interchangeable between the early and late Pathfinders. I picked up a rear flare off a square-dash '93 and it would not bolt up to my '95. Different attachment style, different mounting tabs on the fender. IIRC I used some of that back to black stuff on mine, and they seem to be holding up pretty well.

This:

Compression test wouldn't hurt anything, but you might just have a coolant leak somewhere else (besides that big hole in your rad). My friend's van had a bad hose that we didn't know about and it would run great until the coolant level dropped, then overheat horribly. If it didn't drive any differently while overheating, and there's no mixing of oil and coolant, I would suspect the hoses more than I'd suspect the head gaskets. Does seem odd that the radiator cap didn't let the pressure out. I guess the hard starting while warm could be the head gasket, but it seems like that would be a single cylinder giving you issues.

That's why I suggested just rotating them, assuming the rear tires are in better shape than the fronts.

Blue smoke is oil. Black smoke is running rich. A dirty MAF makes the car run lean (at least it did on my friend's Buick). Dying when you open the throttle sounds like a fuel issue to me, like it can't keep up with the demand and leans out until it dies. +1 on the fuel filter if you haven't done it yet. I guess it could also be the pump or the regulator. Actually, have a look at the vacuum line going from the back of the intake to the regulator, that thing was hard as a rock when I changed it on mine and I'll bet it would give you all kinds of trouble if it broke off.

The tranny is clearly going into third gear, which is its fail-safe. This suggests that the transmission computer has found a fault. If it was just the transfer case binding up, shifting manually into lower gears would not be necessary or helpful. You can download the factory service manual from here. The AT section has a bit where you can decode the flashes of the power mode switch to tell you what made the computer go into limp mode. That'll tell you what to fix. Hopefully it's something simple.

You may have a hard time getting $4500 for a rig that's not quite roadworthy. You might try a tire rotation (put the rear tires that aren't knackered up front), and possibly a DIY alignment (just to get the toe somewhere close to right) and see if that does the trick. It would still need new tires and a proper alignment job, but I imagine "needs tires and alignment" is probably an easier sell than "I'm not sure what it needs, but it's not safe to drive."

Maybe there's a really confused tweaker in your neighborhood who thinks your lug nuts are left hand thread. Is the wheel damaged at all around the mounting holes? All I can think of is that the wheel's not seating right, or the lug nuts are bottoming out on the studs, and the wheel's knocking the studs around.

Maybe the battery or connection is weak enough that when you start it, and the voltage drops, the power feed to the internal memory drops too low?

I've had mine stick in 4HI before (IIRC the engagement is driven into 4x by the shifter, but driven back out by a spring so it won't disengage under load and strain the teeth), but I've never had it engage on its own. The fact that the light's not coming on makes me think that maybe there's something broken inside the transfer case itself, allowing the 2-4 engagement bit to move without the rest of the linkage moving. Maybe that return spring failed? It's been a while since I looked at the exploded diagram. Just to rule out the linkage, watch it from underneath if you can and have your friend work the transfer shifter from 2H to 4LO and back and see if anything seems loose or broken.

Does it move in any gear? How's the fluid look? Also make sure your transfer case shifter or dial isn't in neutral.