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Part Time Light

Tinse4

NAXJA Forum User
Location
Tucson
Ok so I am new to the Xj. I sold my Yj and went bigger due to a new baby. So I bought a 90 XJ 4.0 automatic. one of many issues is the Part Time light is always on. I know for a fact it is not engaged because i just got the 4wheel drive to work. Had a vacuum issue. I am famillier with the I6 and transfer-case, but not the AW4 or all the lights and whistles. Any idea why the light would stay on? Thanks
 
there is a switch on the passenger side of the t-case, it is often mis-categorized in parts store catalogs as a neutral safety switch but its only purpose is to tell the PCM what gear the tcase is in. if it is not connected or malfunctioning it could cause your problem.

it looks like this:

275041.jpg


488131.jpg



hope this helps. NAPA part number for that switch is #FWD21 and that should be the one that fits your 1990 XJ. earlier ones were vacuum operated and had 4 vacuum lines going to them instead of a connector with 2 wires.
 
Thanks for the response. I was working on my t-case today. It does have four vacuum lines that go into the back side of the t-case. It wasn't engaging the front axels due to a vacuum issue. We got that to work, but still have the light. I am wondering if the previous owner did a swap with an older unit. The tag is gone so I can't get any info. I know he had a donor. I got an extra transmission with it also. So maybe it's a communication or lack there off causing it. Will look for another sensor tomorrow when I change the trans guild and filter.
 
Actually on the XJ the PCM doesn't get any feed from the transfer case indicator switch, and the switch is on the driver side on the top, pretty much right over the shift lever linkage connection to the transfer case. It's annoying to get at when it's in the vehicle, make sure you clean the mud/dirt away from the hole before unscrewing it.

With a vacuum unit, the indicator switch is a vacuum switch or something, it's somewhere on the passenger side of the engine compartment. I forget exactly where. Trace the vacuum lines from the vac disconnect on the axle to wherever they go and one of them will probably go to the tcase, the other will go to the vac switch iirc.
 
Ok--lets start over.

1. What transfer case do you have--NP 231 or NP 242?

2. If you have the NP 231 then the circuit is electrical lamp-to-firewall switch-then vacuum to CAD motor on right side of front axle. If you have NP 242 the circuit is electrical from the lamp to the transfer case.
 
Ok so curiosity got to me. I crawled under it here at home. There is a two wire harness that runs on the driver side of the t-case. It is not hooked up to anything currently. Obvious issue. Second on the transfer case I can't find a spot to plug it into. Another obvious problem. Third there is no tag on the transfer case. As far as I know it should be on the flat spot at the rear of the case on the driver side. I am assuming its a 231. The shifter is 2-n-4hi-4lo. There is at the back of the case a four hose vacuum connection. Today at the shop we have I put it on the lift and found a vacuum issue with the front axle. It was not engaging the axles. Fixed it now 4wheel drive works. Again I don't know if the t-case was swapped before I picked it up. Tomorrow doing a trans service with new motor and trans mounts. I will see what I can see at that time. Thanks folks.
 
Ok.

Your shift pattern is NP231.

That means there is a vacuum switch on the transfer case, and a vacuum motor to engage/disengage the CAD axle if it hasn't been swapped out.

At the Transfer case you would have a vacuum supply, and two vacuum out ports--one to engage the CAD axle, one to disengage.

On the vacuum motor on the CAD axle there are three ports--one to engage, one to disengage, and both of those run back to the TC. The third port is for the 4wd lamp--it runs up the firewall to a vacuum/electrical switch, and from there the circuit is electric to the lamp.
 
Thanks Joe. That helps me out.,while I am diggin into her tomorrow I will look for it. Thank again to all the help. Once this issue is resolved its on to the next. There will be no shortage of them.
 
Thanks Joe. That helps me out.,while I am diggin into her tomorrow I will look for it. Thank again to all the help. Once this issue is resolved its on to the next. There will be no shortage of them.

Jeeps--you CAN live with them; you just can't drive them without fixing things!

Good luck.
 
and the switch is on the driver side on the top, pretty much right over the shift lever linkage connection to the transfer case.

i have no idea why I said it was on the passenger side, Ken is correct it is on the drivers side.

brain fart :doh:
 
Boom

My vac is disconnected, CAD is locked. Passenger side fender close to the firewall.




I can't diagnose a blown head gasket...but I CAN post pictures.

:)
 
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Image provided by Cruiser54
 
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