2nd Gen Non-Engine/Transmission 4WD dash light is not working

[Jim Ross]

Shifted into 4WD and noticed my dash light did not come on. I was on a dry dirt road, no water involved and never had any problems in the past. I took a quick look under the truck and didn't notice any wires hanging down or anything out of place. My truck is an AT ('01), where should I look first for the problem?

 

[PWeber]

Could you tell if the powertrain was actually in 4x4? This same thing happened to my 1996 one time. The 4x4 is actually engaged by vacuum, then a switch on the axle turns the light on. (At least on my 1996) I had knocked the vacuum line off the TEE up on the firewall by the brake booster when I changed the fuel filter. Put it back on, it worked.

 

[Jim Ross]

4WD works just fine, both Hi and Lo range, but no dash light.

 

[Extreme1]

So if you turn a sharp corner on pavement with it in 4x4 you get the bind up and crab walking?

 

[KenHokie]

The same thing happened with my previous truck ('00 Ram 2500, V8 gas). The vacuum line that runs the front axle disconnect had fallen out of a clip and melted on one of the exhaust pipes. To see if your front axle is engaging / disengaging, shift into 4x4 then pull the truck into the driveway and jack up both front wheels. If the front drive-shaft turns when the front passenger wheel is spun then the axle is engaged. If not, then you most likely have vacuum problem. A very common problem with our trucks.

 

[illflem]

If your front axle is engaging as you say the problem is most likely a dirty electrical connector down on the axle shift collar. Other problems could be a bad switch on the axle or a burned out bulb.