How to retain 4WD light with passenger solid axle shaft upgrade


Staff Member
Sep 28, 2015
Salem, Oregon
o, you've gotten tired of fixing your Center Axle Disconnect (CAD) actuator motor, or you decided to just fix the problem before it was a problem and replaced it with a solid passenger axle shaft! Great! But now your 4WD light doesn't work. Well that sucks :(. If you have a junkyard nearby and can read this howto, you can fix this problem rather quickly and easily for just a few bucks! or if you want to go buy brand new stuff you can do it for about $50! I'll explain how the vacuum system for the CAD works so you'll get a pretty good understanding of the hows and whys.

The 4WD Indicator Light in the 91-95 YJ is the gauge closest to the drivers side in the center gauge cluster, to the left of the fuel gauge as pictured below. "4WD" With a graphic of the drivetrain will appear in the upper half of the gauge, the bottom half is not used.


In the 87-90 YJ the 4wd light is in the center of the dash along with the seat belt, parking brake, and high beams. Pictured below.

How it works:

To understand how this light becomes lit up when you shift your transfer case into 4wd, can be a bit tricky! It's not necessary to understand exactly how it works, but it will help you make sense of this workaround.

It all starts in the transfer case, the 4WD Vacuum Control Switch is located on top of the transfer case, if viewed from the back it is to the right of the shift linkage. You should see a rubber bushing with 4 tubes coming out.

Red is constant vacuum source to the transfer case
Yellow uses vacuum to engage the shift motor on the front axle CAD
Green uses vacuum to disengage the shift motor on the front axle CAD
Blue is release for the vacuum change, which will release vacuum in the unused hose

When the transfer case is placed in 4Hi, the 4WD Vacuum Contol Switch will send vacuum being produced by the intake manifold though the Red line, down the yellow line and engage the shift motor. Once the collar successfully engages, the indicator switch on the vacuum motor will relay to your 4WD light in the cab, to turn on.

Success! Now we somewhat sorta know how this works! So if you've replaced your 2 piece axle shaft with a solid shaft, regardless of how you dealt with closing off the CAD, even if you left everything hooked up as it was before, its advised you follow these directions to make sure you don't lose your 4wd light, or if you already ditched the vacuum lines, you've lost the 4wd light already!

What you need:

A TJ or 95+ XJ 4WD Indicator Lamp Switch:

OEM Replacement Part Number: J8134473
O'Reilly's Part Number: FWD24
Autozone Part Number: SW2204
Or just go grab one off the transfer case on the above mentioned vehicles at your local junk yard!

A specific pigtail connector to plug into the new 4WD Indicator Lamp Switch:

O'Reilly's Part Number: PT186
Autozone Part Number: 259
Or again, snag it off the wiring harness connected to the switch you get at the junkyard!

Lets get started!

First lets assume you have already swapped out the shafts and taken care of the vacuum lines! You should still have the 2 pin pigtail that was connected to the old vacuum shift motor housing.

1. Cut the connector off the pigtail that used to be connected to the shift motor housing

2. Splice in new 2 pin pigtail (PN: PT186 / 259, see above) (Soldier and heat shrink is recommended)

3. Test fit the new 4WD Indicator Lamp Switch (PN: J8134473 / FWD24 / SW2204, see above) onto the new 2 pin pigtail.
Note: You may need to modify the 4WD Indicator Lamp Switch as it is meant for a plug that can only be inserted one way. It has a small protrusion inside the connector that may need removed so the switch will work.

4. Remove old Vacuum 4WD Vacuum Control Switch from transfer case (location noted above). Move the rubber gasket up off the switch and use 1-1/16" wrench or deep wall socket to unbolt.

5. Replace with new 4WD Indicator Lamp Switch using 7/8" wrench or deep wall socket, plug new 2 pin pigtail into switch. This will require you to relocate this portion of the wiring harness up and over the transmission back to the transfer case.

6. Before securing the wiring, check and make sure everything is working. Turn key to on position and make sure transfer case is in 2hi, then switch to 4hi, the light should now light up.

7. If you haven't already, Plug the vacuum source on the intake manifold with 1/8" vacuum plug
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Reactions: jeepjoe43


Supporting Member
Dec 29, 2021
Dallas, TX
Hey Chris. Wasn't able to send you a PM (probably because I'm new). Will this work if I have a Posi-Lok cable-operated actuator? I think the Posi-Lok completely replaces the vacuum actuator so maybe not? I like the Posi-Lok but I'm just starting to take my YJ off-road a bit and it would be nice to have confirmation that I'm in 4WD.