1990 4 wheel drive indicator

i am new to jeeps and most car work, i have a 1990 and the 4 wheel drive works but the indicator light doesn't come on, all wires look connected and the bulbs look good, any ideas?

How did you check to make sure the front differntial was actually engaging?

Dean

I had a buddy watch the front driveshaft spin when i put it into 4H, also i have driven it in snow and mud and have noticed a difference once i put it into 4H

Might just want to replace that bulb anyway, couldn't hurt. Juice

On this vintage Jeep, there is a vacuum disconnect on the front axle. In 2WD, the right axle shaft is disconnnected, allowing the front to partially freewheel. When the transfer case is shifted into 4WD, a vacuum switch in the transfer case engages the right front axle shaft. You can be "in 4WD" as far as the transfer case is concerned, with without that axle engagement, it isn't actually getting to the wheels. So as DDC XJ notes, your first job is to determine that you are really getting 4WD at the wheels. Loose or rotten vacuum lines, a poor vacuum switch at the transfer case, or a bad vacuum motor on the axle, can all prevent it from working right.

Assuming that the 4WD is truly engaging (that is, the vacuum motor on the axle is engaging the axle), the indicator light is powered by a vacuum switch located somewhere on the right inner fender, which is fed by the vacuum motor on the axle. Check that the vacuum line from the axle shift motor is connected, and that the vacuum switch is working.

The first thing, though, is to be sure that the axle is really being engaged.

How should i determine if I'm really getting the 4 wheel drive at the wheels?

get all 4 wheels off the ground and put it in 4wd and then put the tranny into gear. If the front wheels are spinning you got 4wd. If they dont spin then you got a vacuum problem, vacuum actuator, or worst case would be a blown differential.

When jacking up your jeep just make sure you use jackstands and don't sahke it too much.

Dean

DDCxj said:

get all 4 wheels off the ground and put it in 4wd and then put the tranny into gear. If the front wheels are spinning you got 4wd. If they dont spin then you got a vacuum problem, vacuum actuator, or worst case would be a blown differential.

When jacking up your jeep just make sure you use jackstands and don't sahke it too much.

Dean

Click to expand...

A simpler and perhaps safer way to do this would be simply to shift into 4WD, all wheels on ground, drive a few feet to make sure everything engages and stop (stop engine too) with it in gear if a stick, in park if an auto. Now jack up only the right front wheel. If the axle is properly engaged, you should not be able to turn the wheel.

i'll give it a try thanks.