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If you need to correct your speedometer due to larger tires, it is more complicated on the WJ that on a ZJ. The ZJ has gears in the t-case that can be swapped out, but the WJ uses the rear ABS signal for the speedometer. And because the ABS signal is taken at the wheels, after the axle gears, my speedo still read way off even with 4.56's.
Motomummy sells the SpeedoDRD module made by 12 oclock labs. They sell and make these for bullet bikes, but model U1 (universal model) works great on the WJ's. It modifies the ABS signal, up or down, to correct for different tires.
I installed the DRD module today...I should have done this years ago! It is nice to have a speedo that reads correctly.
The first thing I did was remove the charcoal canister to give room to work with more of the wires. I then unplugged the harness from the ABS module, peeled back the harness cover, and found the wires:
- Black with orange stripe wire in harness - strip insulation away but do not cut the wire - connect DRD's black wire
- Blue with pink stripe wire in harness - strip insulation away but do not cut the wire - connect DRD's red wire
- White with orange stripe in harness - cut the wire, and strip insulation from each side - connect DRD white wire to ABS module side, DRD blue wire to body side (Green w/Yellow stripe on newer WJ's)
The two first wires are power/ground, and the other two connect the ABS signal and modify it. I will not post how to program it here, because they have great instructions with the module and on their website. It took me about 2 minutes to program it...very easy to use. You don't need any special equipment or electronic skills, there is a button on the module. You use that button, and count flashes on the LED's on the module, it is easy to program.
Factory wires ready to connect:

DRD wires connected to the ABS harness:

After a quick test run, I soldered the wires to the harness. This pic shows one soldered, and the others soldered and covered in electrical tape. I currently have it set to a correction of +16.8 but may change it to 16.6 to dial it in a bit more, I need to do another freeway speed test. I am using two different GPS apps on my android to dial it in. I did notice that the speedo stays at 0 until I hit about 3 mph or so, and it also floats at 3 mph for a split second after I stop. Not that I am concerned about the 1-3 mph range, so I am not worried.

I then covered the harness with the factory sheath, covered in new electrical tape, and routed the DRD module away from the abs module.

The DRD module is now placed up against the firewall, just behind the master cylinder and brake fluid reservoir. It is very small, about 3/4 of an inch wide by 1&1/4 of an inch long, with a wire tail about 12 inches long. $70 to fix the speedo, well worth it.

Thanks to Moony, TheKSmith, (both on Jeepforum) for providing me with help as I did this!
Motomummy sells the SpeedoDRD module made by 12 oclock labs. They sell and make these for bullet bikes, but model U1 (universal model) works great on the WJ's. It modifies the ABS signal, up or down, to correct for different tires.
I installed the DRD module today...I should have done this years ago! It is nice to have a speedo that reads correctly.
The first thing I did was remove the charcoal canister to give room to work with more of the wires. I then unplugged the harness from the ABS module, peeled back the harness cover, and found the wires:
- Black with orange stripe wire in harness - strip insulation away but do not cut the wire - connect DRD's black wire
- Blue with pink stripe wire in harness - strip insulation away but do not cut the wire - connect DRD's red wire
- White with orange stripe in harness - cut the wire, and strip insulation from each side - connect DRD white wire to ABS module side, DRD blue wire to body side (Green w/Yellow stripe on newer WJ's)
The two first wires are power/ground, and the other two connect the ABS signal and modify it. I will not post how to program it here, because they have great instructions with the module and on their website. It took me about 2 minutes to program it...very easy to use. You don't need any special equipment or electronic skills, there is a button on the module. You use that button, and count flashes on the LED's on the module, it is easy to program.
Factory wires ready to connect:

DRD wires connected to the ABS harness:

After a quick test run, I soldered the wires to the harness. This pic shows one soldered, and the others soldered and covered in electrical tape. I currently have it set to a correction of +16.8 but may change it to 16.6 to dial it in a bit more, I need to do another freeway speed test. I am using two different GPS apps on my android to dial it in. I did notice that the speedo stays at 0 until I hit about 3 mph or so, and it also floats at 3 mph for a split second after I stop. Not that I am concerned about the 1-3 mph range, so I am not worried.

I then covered the harness with the factory sheath, covered in new electrical tape, and routed the DRD module away from the abs module.

The DRD module is now placed up against the firewall, just behind the master cylinder and brake fluid reservoir. It is very small, about 3/4 of an inch wide by 1&1/4 of an inch long, with a wire tail about 12 inches long. $70 to fix the speedo, well worth it.

Thanks to Moony, TheKSmith, (both on Jeepforum) for providing me with help as I did this!