2000 XJ C100 Harness Wiring Diagram

[Varnish]

I'm deep into a obd2 4.0 swap from a 2000 cherokee into a CJ. I've only got the drivetrain xj FSM and it doesn't have a mapping of the C100 harness (the large square white harness under driver's side dash). Anybody got a mapping they could post up that has the pinout/color/function of this main harness under the driver's side dash that runs into the engine compartment. Its basically the equivalent of the bulkhead connector on the older jeeps. I've already weeded out the items I could trace out from my FSM but have many left over that I don't think I'll need. Appreciated.

I'm slowly piecing a picture of this thing together from individual diagrams but it is very time consuming so if anybody has a one-stop shop for this harness it'd be awesome.

 

[kastein]

Can't help you directly, but what I did was strip the XJ harness down (pulled the wiring for cruise control, front lighting, horns, windshield wipers, washer fluid level sensor and pumps, ABS, heated defrost grid, etc out of it) then look up each of the remaining wires one at a time and figure out what they did. Only took about one afternoon of muttered "WTFs" and a couple pages of notebook paper. I put a 94/95 XJ drivetrain into an 87 YJ with a CJ7 dashboard swapped in... was fun, learned a few things the hard way.

As a side note, you are going to have some fun with your VSS. You'll need a VSS to make the ECU run right when shifting and decelerating (and also to keep it from setting the CEL, though I doubt you'll care about that), and a mechanical speedometer gear housing to drive the CJ speedo, and you can only put one in the transfer case at a time since there's only one mounting hole. What I did was use the cruise control VSS out of an 87-90 XJ, it's behind the instrument cluster (make sure you keep the little black double threaded nut that makes a second speedo cable screw onto it) with a signal converter circuit that makes the 8 pulse per revolution variable reluctance / 2 wire sender look like an 8 pulse per revolution hall effect / 3 wire sender to the ECU, which is what 93 or so and later XJ ECUs want. I based my circuit off an LM1815 and a CD4041UBM buffer chip, if you want a schematic I can throw one together for you. All the chips and resistors/capacitors/etc I used ended up costing around $8 and you can breadboard it pretty easily.

If you're looking to make a factory tach work, you can probably get it going by using a couple switching diodes off the individual coil rail drivers on the ECU to diode-OR the signals together and feed a factory tach intended for a 6cyl, assuming the factory CJ 258 tach was fed off the negative side of the ignition coil primary.

Another gotcha - at least on a 94/95 donor, you DO need the fuse for the heated defrost grid to be installed, that fuse also feeds the starter motor solenoid! Without it, it won't even crank. I'm not sure if a 2000 PDC is set up the same way, double check it.

edit: technically this is probably supposed to be in "other tech" not "OEM tech" - moving it now. Let me know or post up here if you need any other info or run into any issues along the way.

 

[Varnish]

Thanks, the weeding out is exactly what I am doing as well.

I have a '93XJ 4.0 in my '88YJ so I have done a swap kind of like this before, the obd2 just has a few more wires. I have the VSS setup the same way I did the other one which is to use a '92YJ VSS to get an electronic signal while also retaining the mechanical speedo. This was a transition year for the YJ where the speedometer was still gear-driven and the computer needed a VSS signal.

Thanks for the heads up on the tach, on my obd1 swap there was a tach wire to patch into but like you state, I recently learned the newer dash uses a bus-style communication which includes the tach so I'll need to figure something out.

Unless somebody has put a diagram together manually, its looking like the FSM doesn't present the information in a nice one-stop diagram so I'll continue plodding through.

 

[kastein]

Cool! Glad you have that part under control, it was a surprise to me and I had to work through it with what I had available.

On the tach, well - that's where you get lucky. The 97+ uses bus style comms, and the 00+ uses a 3-coil wasted spark coil rail, but the older tachs use the negative primary on the ignition coil. On a 97-99 you could just tap that one wire and be done, but on the 00+ you've got 3 wires to tap, then use a diode from each (to prevent crossing all the coil drives to each other) to the one wire to the tach. At that point, you should have the same number of pulses per rev as an older single coil 6cyl tach would expect. You can simply ignore the comms bus for the cluster entirely then.

 

[sidewaysstarion]

... or, you could just populate the tach out pin on the ecu and run that to your tach.

 

[kastein]

How many pulses per revolution is the tach output on the ECU? When I tried that, I got a wonky reading that didn't line up with what I expected, though admittedly that was on an OBD1 SBC not an OBD2 JTEC. I mean, there's a substantial chance of me being wrong here, but when I tried it it didn't work out well.

 

[Varnish]

Which is the tach-out pin?

I have been reading some pretty definitive accounts that said there simply is no tach signal on the 2000. The pcm gets a crankshaft position/camshaft position pulse but between the the three coil packs or fuel injector pulses nothing translates to a tach signal a traditional gauge can use. The tach in the gauge cluster for this XJ is just data bits along with other information from the pcm.

Since it isn't a must-have I've put the tach project on the back-burner til it is running.

 

[kastein]

It's pin C31 according to my info, on a 96, which uses a JTEC but is still non CCD/bus based instrument panel comms. I'd have to guess it's the same on the following years, but I'm not sure, sideways knows way more than I do about that.

 

[Varnish]

It's pin C31 according to my info, on a 96, which uses a JTEC but is still non CCD/bus based instrument panel comms. I'd have to guess it's the same on the following years, but I'm not sure, sideways knows way more than I do about that.

It appears to have changed. '96 would have still had a distributor instead of the multiple coil packs of the '00.

I think I've got everything mapped out. For future searchers, the juicy ignition-related wires are in C1 and C2. C100 did have the brake switch and obd2 port wires which were worth keeping and it was nice to weed out dozens of other unnecessary wires from the harness. We'll see how I did when I put juice to the whole thing here soon.

 

[sidewaysstarion]

I don't remember exactly which pin it is, but I know if the same pin that the 96 used, I populated it on mine and I was to hook my autometer tach up to it and set it up for 6 cylinder and it read correctly.

 

[Varnish]

While not free, this looks like a decent option for the tach:
http://www.msdignition.com/Products/Accessories/Tach_Adapters/8913_-_Tach_Driver,_DIS_Ignitions.aspx

 

[Varnish]

I ended up using the msd tach driver along with a crown cj tach replacement. The stock CJ tach doesn't accept a standard tach signal but rather measures the pulses from the coil power wire which runs through it. The aftermarket crown tach that has the same size and look of a stock cj tach has the traditional green tach signal wire. One gotcha on the msd tach driver was that the coil pack power wire on the XJ is shared by the fuel injector power wire and the fuel injector pulses were messing with the tach driver. I had to draw the coil pack power from a different source, run it through the msd driver, and then on to the coil pack - I am using the CJ's old cpu power wire and it seems to be working.

 

[kastein]

BTW, there is a real easy solution to the goofy VSS issue I mentioned earlier. Grab the VSS for/out of (I ended up using a junkyard one) an 88-93 Dodge Dakota. It has a standard 7/8-18 speedo cable input that goes right to the d300 or RENIX era np231/242 speedo takeoff assembly, and on the back, it has a nipple for a 5/8-18 speedo cable output. So you can plug the CJ's speedo cable directly in to the back of the VSS. The same sensor can be found on 91-92 or 91-93 (I forget) YJs, too.

You'll need a speedo cable that goes to a 5/8-18 thread on the tcase end as well as the gauge end, but that's easy to get made. And if you want to be cheap, find a RENIX era XJ in the boneyard with cruise control, a 5/8 to 7/8 bushing will be screwed onto one end of the cruise control VSS hidden in the dash.

From there it's as simple as converting the 2 wire reed switch sender to the 3 wire hall effect sender that the 93/94 or so and later XJ ECU wants. Wiring:
sender BK/LB -> XJ harness BK/LB
sender WT/OR -> XJ harness WT/OR
Add a 240 ohm (or so) resistor from XJ harness OR to XJ harness WT/OR as a "pull-up" and you are done.

I was getting an intermittent CEL still on the 87 YJ I helped convert, either heat was getting to the circuit I built or the ECU was pitching a fit about the pulsewidth at lower speeds, I'm not sure. But the replacement using the Dakota/YJ sender and resistor has been in the jeep for ~500 miles now with no issues.

You probably don't care about a CEL but at least with a standard transmission we were seeing issues with the engine bogging when the clutch was actuated while moving. They seem to have gone away with the VSS now installed and working properly.

EDIT: durr, I just reread the thread and you are the person who told me about this VSS swap trick. Disregard, I forgot about that :dunce: I used a Dakota sender as the early Dakotas are much more common in the boneyard here than YJs, but they're literally the same part from Chrysler.

Did you use a pull-up resistor or did it work without it?

 

[Varnish]

Did you use a pull-up resistor or did it work without it?

No resistor, just used 2 of the three wires like I did on my prior swap, I'll let you know when I'm on the road, hopefully in the final stretch here and will just be a few more weeks.