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

Chris

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So, 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.

9136e33dd824.jpg



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
 
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.
 
Chris,
I’ll need to check this out! My 4WD light is ON when in 2WD and OFF when in 4WD. I was thinking the positive and negative wiring were reversed in the switch?
 
Chris,
I’ll need to check this out! My 4WD light is ON when in 2WD and OFF when in 4WD. I was thinking the positive and negative wiring were reversed in the switch?
Not how that works. The 4wd light bulb is powered all the time with ignition power. the bulb's ground runs out to the front axle. When the vacuum CAD moves the fork over, the switch is closed and lets the bulb ground flow to the ground source and then the bulb lights up. If your light is actuating opposite of when it is supposed to, I would suspect your vacuum lines are flipped and operating the CAD fork opposite of when they're supposed to. Meaning your 4WD is not working when it's supposed to either.

Verify if you even have the vacuum setup anymore.
 
Not how that works. The 4wd light bulb is powered all the time with ignition power. the bulb's ground runs out to the front axle. When the vacuum CAD moves the fork over, the switch is closed and lets the bulb ground flow to the ground source and then the bulb lights up. If your light is actuating opposite of when it is supposed to, I would suspect your vacuum lines are flipped and operating the CAD fork opposite of when they're supposed to. Meaning your 4WD is not working when it's supposed to either.

Verify if you even have the vacuum setup anymore.
Interesting. The 4WD definitely seems to work, as I have had it off road and engaged Hi and Lo. All the vacuum lines appear to be connected (can’t say if they are correctly). I will have to watch some more videos on how to remove them again.

Thanks for the info!
 
Interesting. The 4WD definitely seems to work, as I have had it off road and engaged Hi and Lo. All the vacuum lines appear to be connected (can’t say if they are correctly). I will have to watch some more videos on how to remove them again.

Thanks for the info!
Take some pics. You can take the vacuum motor off and observe its operation also when you put the Jeep in 4wd. It’s common for the vacuum lines to crack and not work properly by now.
 
Take some pics. You can take the vacuum motor off and observe its operation also when you put the Jeep in 4wd. It’s common for the vacuum lines to crack and not work properly by now.
Did the CAD delete a few weeks ago and went wheeling again. 4WD definitely working now. I also cleaned up the front diff cover, removed and changed fluid. Pretty nasty in there. Rear diff fluid coming up soon!
A0062112-1698-45D1-9CA4-94C59D644A17.jpeg
37DF2E1B-BA26-4460-A48C-4D25B30478A8.jpeg
80445EAB-C719-44BE-99D2-9D5A0C4B2D7B.jpeg
 
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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.

View attachment 115552


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
I have an 87 YJ 4.2L with BA 10/5 tranny and NP231 transfer case. What I have currently is a plugged off vacuum 4WD indicator (pic 1) and the vacuum off the intake tied into the ac vent vac line. The other four vac lines are gone and the one at the vac switch (pic 2) on the fire wall is cut about 6" out from the pump. I also have a attachment screwed into the CAD housing that has two phillips head screw presumably for wire connection. (See pic 3). The posi-lok cable does engaged and disengage as needed and I have no 4WD light on the dash, which I'm trying to get back.
I have ordered the indicator lamp switch you indicated and the connector as well. Will the two wires from this part run to the two phillips screw heads at the CAD and then back to the two wires at the vacuum switch on the fire wall? The two wires at this location are black, which grounds to the screw above the pump. (see pic) and the other is yellow and black that I have not traced yet. It runs into a harness nearby under the battery.

switch at CAD cable end.jpg


vac switch at fire wall.jpg


vacuum 4WD indicator at transfer case.jpg
 
I have an 87 YJ 4.2L with BA 10/5 tranny and NP231 transfer case. What I have currently is a plugged off vacuum 4WD indicator (pic 1) and the vacuum off the intake tied into the ac vent vac line. The other four vac lines are gone and the one at the vac switch (pic 2) on the fire wall is cut about 6" out from the pump. I also have a attachment screwed into the CAD housing that has two phillips head screw presumably for wire connection. (See pic 3). The posi-lok cable does engaged and disengage as needed and I have no 4WD light on the dash, which I'm trying to get back.
I have ordered the indicator lamp switch you indicated and the connector as well. Will the two wires from this part run to the two phillips screw heads at the CAD and then back to the two wires at the vacuum switch on the fire wall? The two wires at this location are black, which grounds to the screw above the pump. (see pic) and the other is yellow and black that I have not traced yet. It runs into a harness nearby under the battery.

View attachment 121602

View attachment 121603

View attachment 121604
It’s pretty simple. The 4WD light is operated by ground. The gauge cluster feeds the bulb ignition power, and the ground is switched closed or open depending on the vacuum 4WD. From the factory, an 87-90 YJ has the little blue vacuum switch on the firewall with two wires connected to it, as you’ve shown. One of those wires comes from the bulb, one goes to ground. When in 4wd, that thing gets vacuum and closes the circuit, lighting the bulb.

The 91-95s are different. They have a simple 2-wire switch mounted straight on the CAD cover. The fork slides over and presses the button on the switch, which lights the light.

When folks install a posi-lok, they receive a switch that threads into the new posi-lok CAD housing. The switch has those two screws as you’ve indicated. This is really more geared towards the 91-95 YJ, which has the 2-wire switch. If a 91-95 owner wired theirs up as the kit intended, then their light will work like factory, which is only when the fork moves over.

The TJ transfer case switch referenced in this thread is for telling you about the transfer case, which is really more intended to use that switch when you have a solid front right axle shaft. In that case, the switch tells you the tcase was shifted, boom, done. With the posi lock it’s weird - do you want to know if the tcase shifted properly, or that you moved the CAD fork properly? Neither alone will give you 4WD, so you have to decide which you’d rather have operate the light.

However you want to do it, the two wires at the blue vacuum switch are where you’ll start. Those need to be extended to the CAD or the tcase depending on which one you want to operate the light.

If you wanted to be creative and make sure the light only comes on once the transfer case is shifted AND the CAD fork is moved over, you could do so by extending the wire for the gauge to the CAD (one of the screws on the posi lock switch), then attach a wire from the second screw and run it to the transfer case using the TJ switch, then you’d run the second TJ switch wire to ground. This way the bulb would not light up until both the transfer case and front axle were shifted into 4wd mode.

I think the reason the factory chose to run the light off of the CAD was for 2 reasons: 1) because it’s the last part in the sequence and 2), if the tcase didn’t shift, you CAD probably wouldn’t engage. With the CAD disengaged, the left axle shaft turns the spider gears and rotates the center axle shaft backwards, while the right axle shaft still spins forwards. That means if you’re going 50 mph, the difference between the right outer shaft and the intermediate shaft are spinning opposite each other by about 100 mph. When the tcase shifts, the driveshaft spins the diff up to vehicle speed which should then synchronize the intermediate shaft up to the right speed and the right direction so that the CAD can engage. So I would imagine that’s why the switch is on the CAD, if the tcase for some reason didn’t actually engage 4wd and start spinning the driveshaft, I would imagine the CAD would have a hard time or possibly impossible time getting the fork to move over with only a simple vacuum suction force.

Hope that helps.
 
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You have made it simple my man! I understand it very well now. Thanks for sending more than just an answer. That helps folks enjoy the project much more.
 
Hi Chris!! So I did the cad delete on my 92 last year and finally decided to do the fix to have my 4wd light again. I watched a few different YouTube videos. I removed all the old vacuum lines and got the TJ sensor and the pigtail switch and did all the wiring. My problem is now my 4wd light is on in 2wd and 4wd. Any thoughts?
 
Hi Chris!! So I did the cad delete on my 92 last year and finally decided to do the fix to have my 4wd light again. I watched a few different YouTube videos. I removed all the old vacuum lines and got the TJ sensor and the pigtail switch and did all the wiring. My problem is now my 4wd light is on in 2wd and 4wd. Any thoughts?
What brand switch did you use?
 
You have made it simple my man! I understand it very well now. Thanks for sending more than just an answer. That helps folks enjoy the project much more.
Got it working! Thanks. It’s the little things sometimes. I thought the TJ switch ball was not far enough out but it works fine.
 
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So the brand is just the Napa brand. Says made in China
I would remove the switch and operate it by hand, watching the dash light to see if the light goes on and off that way. Then that tells you if the switch you bought is faulty or if it doesn’t reach the transfer case internals properly.
 
I have an ‘88 YJ. My 4WD CAD and light didn’t work when I brought it home 4 yrs ago, among a lot of problems that weren’t addressed. I found that the primary vacuum source line off the engine was connected to a dead vacuum port. So I hooked it to a primary manifold vacuum port, and all works correctly now. I was lucky.
 
Delete the body lift. The tension in the rubber caused by the body lift is keeping it from shifting and staying in gear properly.