4WD Light

[Mainsail]

OK, what does the yellow 4WD light tell me?

Shift lever is in 4WD

Transfer case is in 4WD

I ask because every so often I shift to 4WD and the light doesn't illuminate. Is the front axle engaged even tho the light didn't come on?

Sometimes the 4WD light comes on a minute or so after I've pulled the lever to 4HI.

 

[nyoffroad]

The light just tells you the position of the lever, it doesn't know if the hubs are locked or not.

 

[Mainsail]

The light just tells you the position of the lever, it doesn't know if the hubs are locked or not.

I know that. What I'm asking is does the light say the transfer case is in 4WD or does it simply say the shift lever is in 4WD.

 

[Barrman]

The sender for the light is on a shift rail inside the transfer case. Which means the light comes on if the shift rail has been moved. Nothing to do with the front axle.

 

[Mainsail]

LOL, well if there are two responses that completely miss my question I guess I failed to articulate my question well.

I only mentioned the transfer case, I didn't mention the hubs or the front axle.

Does the 4WD light indicate that both output shafts are turning, or does it merely mean the shift lever for the transfer case is in the 4WD position?

or...

If the 4WD light is out while the shift lever is in 4HI, is the transfer case in 4HI?

or...

If the 4WD shift lever (the one with the black knob on the floor closer to the passenger) is pulled rearward to the first stop, but the yellow 4WD light does not illuminate (and the associated bulbs and wiring are fully functional) , is the transfer case in 4WD (attempting to send twisty power forward) or not?

 

[Barrman]

Sorry for the short reply last night. I was tired and just did the basics.

I think you have the aluminum NP208. You didn’t state though. The NP208 has a single shift shaft that changes front axle engagement first and then neutral and finally low range. The sensor for the light has a spring loaded ball on the end and that ball sits in a little detent on the shaft while the transfer case is in 2 wheel drive. Which means 99% of the time the contacts inside the switch are open and have been open for almost 40 years.

As soon as you move the shaft, the ball gets pushed into the sensor and is supposed to close the contacts which will send power to the 4x4 light. Those contacts weren’t super high quality when new. Now that they have spent decades being ignored and not used they are very iffy. That is why your light sometimes pops right on and sometimes takes a moment or two to get the electricity through. Since there is only 1 detent on the shaft for the switch. The light is supposed to be on anytime you have moved the shifter out of 2 wheel drive hi. It doesn’t know what Rangel or level of engagement you have selected.

Going back to 2 hi then brings the old spring and probably gummed up ball into play. There isn’t your arm moving a solid steel shaft to make it move. Just an old spring supposed to push it down. Sometimes that doesn’t work to fast or even at all. The only way to know for sure that you are back in 2nd is to unlock one hub and try spinning the drive shaft from the transfer case to the front axle. The drive shaft should spin free at the transfer case and the axle shaft for the side you unlocked should spin. Don’t forget to unlock the other front hub and drive on.

If you have the cast iron NP205. It has two shift shafts. I will have to look at mine in my class on Monday. But I think the sensor, if there is one at all is on the shaft that engages the front drive shaft. But, unless you have set it up to be a twin stick shift. The linkage will engage that before it changes the hi/lo range shaft.

Does this answer your question better?

 

[Mainsail]

Good point!

Forgot to mention - stock M1009.

So the light just tells me the desired condition (4WD) not the actual condition.

It always goes off with the lever in 2HI. It almost always comes on when the lever is pulled to 4HI, but sometimes there's a delay. It might come on a minute or two later.

When it doesn't come on like it is supposed to, I reengage the 4WD, jiggle the lever, and hope the truck is in 4WD. What you're saying is the transfer case IS in 4WD even if the light hasn't come on, so I don't need to fiddle with the lever.

 

[Barrman]

Well, that is a loaded question. If the light come on it means the shaft has moved. It doesn’t’t mean 4x4 is engaged. Your linkage to the shaft could be out of adjustment to get 4x4 all the way engaged. Or, the little plastic pads on the shift forks could be worn or totally missing. Either will cause the light but not proper 4x4 hi or low engagement. The shift fork pad problem could also cause the light to be out but 4x4 not all the way disengaged.

 

[cucvrus]

Go under the truck unplug the 4WD switch. Jump the 2 wires with the key on. The light in the dash should light. If not, it could be bad bulb, bad, dirty connection at the printed circuit board, bad dirty socket, pinched wire. But the switch is 7/8" and they do wear out. The same switch was used on old Chevy's with manual transmissions for the B/U lamps. It is just a spring-loaded ball that is depressed when the eccentric of the transfer case lever depresses the ball and completes the ground and the dash light lights. Not all correct terminology but right to the point.

Click to Enlarge

(Read Reviews)
1981-1986 Chevrolet K10 - Four Wheel Drive Indicator Lamp Switch - Standard Motor

 

[LT67]

LOL, well if there are two responses that completely miss my question I guess I failed to articulate my question well.

I only mentioned the transfer case, I didn't mention the hubs or the front axle.

Does the 4WD light indicate that both output shafts are turning, or does it merely mean the shift lever for the transfer case is in the 4WD position?

or...

If the 4WD light is out while the shift lever is in 4HI, is the transfer case in 4HI?

or...

If the 4WD shift lever (the one with the black knob on the floor closer to the passenger) is pulled rearward to the first stop, but the yellow 4WD light does not illuminate (and the associated bulbs and wiring are fully functional) , is the transfer case in 4WD (attempting to send twisty power forward) or not?

Sometimes the light works, sometimes it does not, so just ignore it...