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Help With Troubleshooting A 4WD Problem with 1990 Trooper?

1630 Views 3 Replies 2 Participants Last post by  Hyunduzu
The day I bought my 1990 Isuzu Trooper it went into 4WD fine and took it off-road for a bit just to see if it worked ok, and it did. The green 4WD light came on too. The next day, I try to put it back in 4WD High but the light never comes on. When I put it in 4WD Low the light still doesn't come on, but I know for sure it switched to low. I also know the bulb isn't bad, because I pulled out the bulb and checked it. Because of my inexperience with 4WD, my question is, if my 4WD isn't working, is it possible to be able to go to 4WD LOW and lower gears clearly engaged without actually being in 4WD? When I go to 4WD low, the gears are very short, so I know it's doing something, but just not sure if it is actually in 4WD.
Does anyone know what actually triggers that 4WD light? Is there a microswitch near the base of the shifter? Or is the switch someplace else? Thanks in advance.
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First thing I would do is find out for sure if 4-hi is engaged or not. Go find some dirt and spin the tires - it will be obvious if the fronts turn too.

People go through alot of trouble to be able to set up their t-case so it can be put into low gear without 4wd - I don't think that could just happen without some major mechanical failure that you would notice.

Judging by the pics in my factory manual, the switch appears to be on the front of the shifter base.

Best case scenerio: if you find that your 4wd is working, perhaps your first offroad test loosened a bad connection at the switch.
Thanks for that info, for sure. I did take it out in the woods and it feels like it is in 4WD and both hi and low seem to work. That indicator light still won't come on though, and I know the bulb is good. The first day I got the vehicle it worked fine, the next day it doesn't come on. I did notice there are 2 wires running parallel to the driveshaft and both have connectors to them, however one wire just ends and doesn't plug into anything, but I don't know where these wires run to.
At least I know 4WD is working now though
Try checking from inside the cab - pull up the shift boot & carpet around it and take a look down in there.

The wiring harness hugs the top of the tranny from the motor and makes its way to the regular gear shifter(neutral switch) and then splits - one side goes to the reverse light switch, the other to the 4wd indicator switch at the t-case shifter.

4wd switch is 2 wires: black(ground) & light green. More than likely you have a bad ground and/or crusty connectors that may have seperated. If you can actually get to it, it should be a simple fix.

Good luck. 8)
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