1990 YJ help

[elevatorman]

OK ,I was trying to assist my friend with his 90 YJ 4.2 Auto Wrangler
Seems the transfer case had gotten stuck in 4WD.
I was able to get it shifting with little or no effort(seems operator error on his part).Now he claims the indicator light on the dash is not working.
He changed the bulb and claims everything was working prior.
Need wiring help or any advice?:???:

 

[fireman32]

mines a 89 yj 4.2 manual, not sure what all changed between 89 and 90, but beside the battery on the firewall there is 4x4 indicator gauge, make sure the vacuum line from the transfer case is attached to it

 

[superj]

yup. that is how my 87 is also. its a little vent looking thing wit ha wire and a vacuum line

 

[elevatorman]

How does that work with the indicator light on the dash?It shifts ok in and out of 4hi and lo and 2wd.He just lost the light on the dash

 

[fireman32]

i believe that when you engage the 4x4 the transfer case creates a vacuum which goes to that switch, opens the switch allowing current to pass through and turn the light on.
not a necessary item, mine isnt hooked up and the 4x4 works fine.
however the (i cant remember exactly what the switch is called) may be bad.

 

[Bounty__Hunter]

How does that work with the indicator light on the dash?It shifts ok in and out of 4hi and lo and 2wd.He just lost the light on the dash

There's a good chance that the central axle disconnect (CAD) in the front axle is not engaged if the 4wd light is not coming on, very common problem with YJ's.

The shift lever only controls the transfer case, the CAD is controlled by a vacuum switch at the transfer case. With the CAD disengaged, you will have 2wd despite the position of the transfer case shift lever.

Find the 2 vacuum lines to the front axle, pull them and feel for strong vacuum alternating between the 2 lines depending on the transfer case shifter being in 2wd or 4wd. If you have good vacuum here, the problem is inside the disconnect housing. If poor vacuum, you have a bad vacuum line or a bad vacuum switch on the transfer case.

99% chance you put that Jeep in gravel, engage 4wd, and neither front tire will spin when the rear tires spin.

For a quick and easy fix, remove the 4 bolts holding the disconnect housing to the front axle. Remove the housing, slide the shift collar over both axleshafts, and reinstall the housing upside down. The shift fork will now hold the front axleshafts locked together.

 

[elevatorman]

Thanks everyone! I fixed it. I hope this explanation can help others.
first I put a jumper on the green and black wire going to the vacuum switch and the dash indicator light came on-bulb ok,then after that I disconnected the vacuum line to the hard plastic lines gong to the axle and excuse me but??(I sucked on it) and light lit up again so I determined the switch was good,
I then determined that it was a vacuum issue and traced and followed the vacuum lines from the transfer case to the front differential etc.and checked and cleaned the "vacuum check valves".
Upon checking these I had stuff blow out of them which seemed to be excessive fuel Reinslalled and eventually the unit was lighting up as new.
I determined after all of this and yet I could be wrong is that during my retiming of the ignition and carb adjusting It may have fed some heavy fumes etc.. into the vacuum lines and clogged some valve checks. Like I said after clearing them it works fine and all I did before it failed was reset his timing and adjust the carb

 

[BDurrant]

OK I did the Nutter Bypass and while I was eliminating the miles of wire and vac hose I found the RED vac hose from the front axle and it was just plugged. I was given the 1989 yj recently and I haven't ever driven in 4wd. my question is, where should the vac for this line come from? I have many ports available from the carb and the manifold.

 

[elevatorman]

Ok Bert,My 87 is the same as my friends 90 and the "hard" red plastic line comes up from the harness goes into a "T" with a check valve. One side goes to the large hose on the canister under the battery,the other end runs up around the rear of the valve cover ,"t's" again with a hard metal line which eventually goes to the manifold port just above the EGR valve.
Both his and mine are smogged in California and pass all inspections.
Copy of routing attached to help you.

 

[BDurrant]

Thank you for the info. I don't have a copy of the vac diagram under my hood, go figure. You say that the line goes to the storage canister then behind the valve cover to a T, one side ends up at the Manifold Vac port above the EGR but where does the other side of the T go. Thanx again