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1990 jeep comanche 4wd Part time light

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Okay guys, you havent failed us with info so far, so here's another question. my son bought this 1990 4wd comanche with the 4.0l and Auto trans. It prett darn rusty but it only has 65,000 miles. So here the question, the part time light on the dash is on, even though it appears to be shifted into two wheel drive. is this possible, or is the truck stuck in 4wheel drive.

Is the shifting into 4 wheel drive, mechanical or is it done via a solenoid that might be stuck.

With all your experience I am sure that one of you must have been through this.

Oh by the way when he bought it the light was not on. It came on after he shifted it into 4wd on the way home with it.

Is there a specific procedure for how the truck is to be put in and out of 4 wheel drive/

Thanks for any insight you can provide.

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Common problem!


The truck likely has a disco front axle. Inside the disconect is a fork that moved a splined collar that engages the two piecs axle shaft on the pass side of the axle.


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Well, whats likely hapening is that the fork is not completely returning to isnt fully dis-engaged position. This funtions via vacuume. Either the tubing has a leak or is unplugged or has a bad part on the T-case.


There is a great write up on how to clean and service this part. I believe it is on the www.madredXJ.com site


Here is a pic of the disconnect you will need to look for:


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The t-case is mechanically shifted, but if the assembly underneath the trucks is loose, then I guess it is possible that you might be stuck in 4wd. Not likely, but technically possible. If I remember right, in older MJs, the light is tripped by a switch in the engine compartment that goes on when vacuum is applied. The little switch could be stuck too.

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sooo, in continuance with the vacuum disconnect...


when i first landed my truck the p-t light worked perfect and it seemed to stop working right after the first time i got it REAL stuck


but luckily its stuck ON not OFF. so i can use 4x4 (well i COULD)

but when I'm on the gas alot (only in gear, not if i revv it up) the light goes off and comes on when i let off the gas...


would you suggest cleaning the disconnect, or checking the vacuum switch in the engine compartment?


1989 btw.

-nick aka pro-threadjacker

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Did have the same problem, the vacuum control switch on the transfer was not working.


Inside the control switch it’s a piston with o-rings, when you put the transfer in 4x4 the vacuum is routed to the shift motor.


The piston was stuck inside the control switch, so when putting the transfer into 2x4, vacuum were still applied to the axel shift motor.


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