Have been having some issues with 4 wheel drive engaging and would like to test some of the various components. Solenoids and indicator look easy to get at. FSM shows the relay possibly in the dash???
So took her for a spin today and 4wheel drive is engaging but the indicator light in the instrument cluster is not illuminating. So does this mean one of 2 thing.
1) Indicator light blown
2) ADD indicator switch possibly bad
94 sr5 manual xcab.

 

https://web.archive.org/web/20120424...26addcontr.pdf
Yes, FSM says "in dash," but I can't tell you where exactly.
But the wiring diagram shows pretty clearly what it does. Put your multimeter on the VSV terminals, and shift in and out of 4wd. The voltages should change as indicated on the schematic. Testing the ADD indicator is easier; just disconnect the leads, shift into 4wd, and short the leads together. That should turn on your light.

 

Thanks for the link.

 

So I was finally able to test the ADD indicator switch and I was not showing continuity when the switch is in the engaged position (4×4 engaged) which according to the FSM it should be showing continuity. Shorted the leads for the 4wd light and it came on, so bulb is good.
Is the ADD indicator switch a type of plunger switch? I'm just wondering if it is possibly stuck and with some cleaning can free it up. If I remove the ADD switch are any liquids going to come out or is it dry. Truck is definitely going into 4wd.

 

You'll get some fluid, its not a sealed system. Acutally I had neglected to properly tighten mine and probably leaked a few oz's before I noticed it.
Its just a plunger connector. Identical to the Reverse light switch and both xfer case switches on the trans.

 

 

We had an issue w 4wd not engaging on my son's 4runner w/AAD. Our initial issue was something with the clutch fork not being installed correctly after I took the AAD shaft out to remove a broken CV axle stub. To fix, I think we would have had to pull the actuator off to get access and ensure the clutch fork and AAD sleeve are lined up correctly. But we had a local shop doing some other work in the front end so they took care of it. More recently the electrical button does nothing when pushed. My son figured out a way (with some help from someone else) to shortcut the vacuum system by moving a vacuum hose from one connector to another, effectively bypassing the electrical bits. You can raise the front right (passenger) tire off the ground to test it out. I know that's not giving you exact answers but maybe it'll help some. Good luck!