According to my 2000 EWD the 4wd light needs the ADD position switch and 4wd position switch to be closed in order to complete the ground circuit. Is it possible you have a faulty add position switch?

Here's the diagram: Dropbox - 2000 4Runner Electrical Wiring Diagram (EWD383U) - Printable - Simplify your life

Thanks for sharing that EWD!

Maybe the ADD Position Switch is faulty, I haven't tested it (yet).

Genuine question, if the ADD Position Switch was faulty, why would the 4WD indicator light behave exactly as it's supposed to from an end-user standpoint? Light off when j-shifter is in H2 position, and light on when j-shifter is in H4 and L4 positions? Or maybe I'm misunderstanding what the switch does.

EDIT: I think I understand. A faulty ADD Position Switch might have been giving me a false positive on the indicator light. If the ADD Position Switch is erroneously closed all the time, then the indicator light will turn on as soon as the 4WD Position Switch is closed. So, it's not that a faulty ADD Position Switch was causing my 4WD not to engage, but rather a faulty ADD Position Switch might cause a reporting error (indicator light on) which served as a red-herring during troubleshooting. If I leave everything in its current state, then everything works from a driver's perspective: 4WD sends power to front wheels, indicator light is on/off at appropriate times. However, the indicator light is actually only reporting on j-shifter position, instead of both j-shifter position and ADD position. Am I on the right track?

As far as I understand it you have it correct in your edit. If the ADD switch has faulted into a closed position then once the transfer case position switch closes in 4HI then the circuit for the 4wd light will be complete.

Excellent, thank you!

@JustTroItIn so a faulty ADD Position Sensor would explain why I was seeing the indicator light, and the click sound I was hearing was not the actuator but rather a relay, I guess?

So, if I do decide to replace the faulty ADD Position Switch, I think I’d need Toyota PN 8422235110

Can anyone confirm the part number and also which switch it is on the photo below? (I'm assuming the ADD Position Switch in on the transfer case, correct me if I'm wrong. If the body was still off the frame, I'd be able to just following the wires...)

The ADD position switch is on the front axle housing by the ADD vacuum actuator if I remember correctly. Let me see if I can find a better picture and part number...

EDIT: Here's the 2000 FSM I reference: Update your browser to use Google Drive, Docs, Sheets, Sites, Slides, and Forms - Google Drive Help Click on section 29 and then SA-26. The ADD switch is in the upper right corner of SA-27

The 'click' you are/were hearing when you shifted into 4WD is likely the relay that is in the passenger footwell that sends power to the ADD VSV's.

There is a chance that a previous owner shorted out the front ADD switch (there is a factory part that does this on the manual hub Tacomas!).

That would explain everything you experienced.

The ADD position switch is located just to the right of the front diff flange in this picture, gray with two pins. It doesn't have any wiring on it since I hadn't wired up my 4WD swap yet.



From there, there is a short harness that runs up to where the vacuum hard lines mount on the top of the front diff (just below the oil filter in this pic), then a plug that runs to the main engine harness. Check in those areas for shorts or damage. If it is shorted to ground, it would act like the ADD is always engaged.

-Charlie

I disagree. If the add switch wiring was shorted to ground then the 4wd light would always be on. The ground path for the 4wd indicator light goes from the indicator to the add position switch to the 4wd position switch to ground.

You are right. I was going off of memory...

-Charlie

Perfect!! Thank you

Just so there's no confusion down the road for people looking at this thread. The switches numbered in this photo are:

1. Transfer L4 Position Switch
2. Transfer Neutral Position Switch
3. Transfer 4WD Position Switch

(VF2A transfer case)

All three of these switches in the photo seem to work fine for me.

Below is the diagram of the front diff with the ADD Position Switch at the top right of page two as @Bad Luck pointed out. Looks like I'll need a new ADD Position Switch and a gasket (still looking for part numbers)

Attached Images

   

I had a problem with my ADD position switch when I first bought my 4Runner. I removed the switch and cleaned it out with electronics/contact cleaner while depressing the "button" (it's more of a ball) and was able to get good continuity when depressed and no continuity when released. Might be worth a try if you haven't ordered parts yet and have a multimeter.

Makes sense that the ADD switch in the diff was bad and the click was the relay. Please let us know if you find the front switch was indeed bad when you get around to it.

Great suggestion. I have the tools and supplies, so I’ll try cleaning the switch before replacing.

That can/does work for the transfer case switches too. And the reverse switch on many manual transmissions...

-Charlie