Finally managed to get cruise working perfectly on my truck, inserting the information here so people don't have to read the entire thread and piece together. I'm assuming this should work for 97-98, I know 99 had a few changes and if anyone with a 99+ with the 3.9 wants to chime in, I'll update this info to include those years. Please check the reference voltage and switch resistances, the parts should be the same, as long as the switches are 2 wire. This might also work for the 5.2, I can't see why the system components would be different.

Equipment:
1998 Dodge Dakota Sport RC
3.9L V6 Magnum
42RE Auto Trans

Required Tools:
Steering Wheel Puller
T-20 Torx (column bezel, switches, and potentially blinker stalk [security torx required])
Phillips Screwdriver (Driver kickplate)
8MM Socket (Airbag screws)
13/16" Socket (Steering wheel nut)
12MM Deep well socket (Servo mount nuts)
Multimeter (ohming switches, checking reference voltage, optional but suggested)

Required parts:
Engine Bay: Check stock wiring, 4 way connector against the firewall, passenger side, by the A/C accumulator. Should be a capped T vacuum connector above it nearby.
There's 2 studs in this area near the cowl, the servo mounts here. You need to pull the Servo mount, Servo, vacuum line, and Cable. Just two nuts on the studs, be sure to grab the connector grommet on the vacuum line to replace the cap on the destination truck. Push the connector on the throttle body to disconnect the cable, two tabs to pull the square mount on the throttle body, pull as one unit. Reverse for install.

Inside Cab: MAKE SURE TO DISCONNECT THE BATTERY. You will be removing the airbag, be prepared by renting a steering wheel puller, should be about $20 at any parts store with their free loaner tool, you'll get a refund when you return it.
You'll require: Switches, Clockspring, and steering wheel bezel. Use a torx bit to remove 3 screws under the column, I would suggest having a safety torx set. Gently pry the two column bezel pieces apart, there's two snaps in the back.
Behind the steering wheel is 2 8mm bolts that hold the airbag and gently pull it out, carefully pop the center connector out, then the top line you may have to cut back the shielding and it has a locking spade connector, push the lock in and disconnect, set airbag aside.
Use the same torx as before to unscrew the two switches, push the square part to unhook the harness from the switch and pull the switches. At the time, I would HIGHLY RECOMMEND ohming the switches to ensure they are in spec (this is what foiled me before).

Ohm specs:
On = 909 ohms
Set = 6650 ohms
Resume = 15,400 ohms
Cancel = 0 ohms
Coast = 2940 ohms

Likely has a tolerance of ~50 ohms or so. After removing the switches, remove the center nut with a 13/16 socket and use the steering wheel puller to remove the steering wheel. Remove the screws in the steering wheel to remove the bezel (non-cruise bezel doesn't have space for switches). BE CAREFUL TO THREAD THE WIRES WHEN REMOVING THE STEERING WHEEL SO YOU DON'T BREAK THE HARNESSES.
To get the clock spring out, under the steering column is one of 2 harnesses to disconnect, under the column, gently pull the plug and lift the black tab, should come out easily. Next, use a phillips screwdriver to remove the 3 screws at the bottom of the driver kickplate, carefully lift and pull forward to remove (press clips at the top). There's a yellow connector to disconnect for the airbag, you'll have to thread this back up to get it out. The clockspring is held in by 2 clipping tabs and lineup pins. The top one is fairly straight forward, for the lower one try to gently wiggle the clockspring to get it to come off, DO NOT FORCE IT. If it refuses to come off, use a safety torx of the same size as before, remove two screws holding the blinker stalk on, remove it to see the other clockspring tab. Remove the clockspring.

WARNING: DO NOT TURN THE CLOCKSPRING WHILE IT'S OUT. Otherwise you will have to follow the recentering procedure. If the steering wheel was not straight on the truck you're pulling from, or you do not know, carefully push the two lock tabs in and turn the center clockwise (there's an arrow on the clockspring showing you this). Gently turn until you get resistance DO NOT FORCE. Do the same in the other direction, counting each rotation until you hit the same resistance, half this number and turn back in the other direction to center. For mine it was 2 1/2 turns from one side to center. This must be centered or you will break the clockspring and you horn/cruise/airbag will not work (your airbag light will come on).

Congrats! You have all the parts required. Follow the same procedure and reverse to install the components, the airbag will be a bit of a pain to squeeze between the switches (remember to swap out the steering wheel bezel!). I suggest ensuring you have the proper reference voltage, the connector in the column in the bottom of the clockspring is where you should test. The signal wire on a 1998 is Gray/Light blue, with the key on you get a 3V reference signal. If you do not get 3V here, you should check continuity on the wire to the PCM connector C3. Put everything together, hook up the battery, go for a test drive. Your cruise light will not come on (Chrysler disables the cruise light in the PCM if the vehicle is not equipped with cruise, however, the system DOES work.) If you want the light to work, you'll have to have the dealer enable the light in the PCM.

Repeating technical references:

Switch Resistances:
On = 909 ohms
Set = 6650 ohms
Resume = 15,400 ohms
Cancel = 0 ohms
Coast = 2940 ohms

Reverence Voltage: 3V

Finally, the wiring diagram for a 1998 for the speed control:



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(original post)
Sadly my 1998 Dakota, RC 3.9, didn't come with cruise control. I'm looking into putting in the factory kit. I plan to hit the yard this weekend and have a general idea of what I require.

Servo, cable, mount, vac line, switches, and clockspring off the top of my head. What am I missing on this list, and does anyone else already have CC and don't mind giving me some images of the required parts and their location. Particularly the servo, I want to make sure mine is prewired before I start this journey. I found two plugs to nowhere under the hood, but I'd like a doublecheck. My brother has a solus so it should in theory be able to enable it in the pcm, otherwise I gotta hit a dealer.

So anyone have done this and has a rundown of required and location pictures? Also if not too much trouble, take pictures of the actual plug harness so I can match. Considering the previous owner put in a different harness for the crank sensor, I wanna check everything.

 

Servo mounts in front/under the air box. 4 pin connector as I recall, one solenoid for charge/engage and one solenoid for vent/release.

 

Hm, when I got it, the truck kinda lacked the factory airbox... Previous owner had put a CAI in it. Mind grabbing me a picture?

 

Did this to my '00 years ago. The harness should already be wired. The only thing that didn't work was the cruise on light on the cluster. The dealer took care of that for $20 with a DRB.

 

Aha! I found a 4 pin plug to nowhere! (it has an unused mating end to seal it). It's hanging out on the firewall beside the ac accumulator, would this happen to be the harness I seek?

 

I'll grab a photo when I head out in a bit.

 

Well, it's accomplished. Hit a junkyard less than a mile from my place, they had TWO Dakotas. a 1994, and a 1999. The 99 happened to have been an SLT V6, score. Pulled the servo, leaving the vacuum line, cable, and bracket attached, switches, bezel, and clockspring. Cost me about $31 and some change, tossed them in my truck. Hardest part was getting the steering wheel off at the junkyard, coaxed it with a hammer... Mine I rented a puller. It was tricky getting my airbag back in around the switches, but it all went in and fit together. Just gotta hope it all works now. entire process, including travel took about 3 hours, trip to junkyard, time there (the truck was IN THE BACK naturally.), getting home, heading back out to get a puller, etc. My brother has a Snap-on Solus Ultra, which was sufficient to reprogram for my tires, so I hope it can also do the cruise. Otherwise, I'll have to search out a dealer, none around here... :/ Despite the light not working, should the cruise control still actually work, just not signaling the light to come on? Or does the light signify to the PCM to enable the function completely and not just a light signal.

 

Mine worked even without the light.

 

Well then that's not a good sign, I took the truck to return the puller and kinda thought to try it despite the light not working, didn't seem to work.

Edit: I'm thinking now.... it's only half wired... It had the wiring for the servo, which had a dummy plug to protect it. So I decided to look again at the clockspring. Took the steering column bezel off to recheck the clockspring harness, noticed it only has 3 wires, whereas the clockspring (including my old one) has five pins. This is not counting the yellow connector I had to feed down, which I assume are the airbag, as my airbag light didn't come on even with the main connector disconnected. My horn works fine, so the clockspring has connection. Anyone mind pulling the bezel off and checking how many wires their connector has?

 

did your clockspring not already have the pass-through pins for the buttons? As I recall they should have, as the option was either radio control or cruise control wheel buttons. They used the same pins on the wheel side, but different on the harness side...I think. Also, i don't see a yellow wire in that plug, sure the 2 airbag wires are not on another connector?