89 2.9 auto trans 4x4 won’t do anything. No lights no clicking, no anything

[Fryesvan]

I’ve got an 89 2.9 with auto locking hubs. I have no 4 wheel lights other than to light up the two push buttons. When I press them, nothing happens at all. No relays clicking or anything that I can tell I pushed the test light on the 4x4cm and it just light up for 30 seconds or so the. Went off. Not sure what that means. I pulled the shift motor and checked for power. At all times I had power at only to of the wires on the harness. The middle one and one other. The truck is insanely clean. I was able to put it in 4hi manually and figure out that it works fine but put it back in 2hi so I could continue to drive it. I bought a used switch to no avail and a used 4x4cm and it just did the same single light up. Any help would be great.

 

[RonD]

Welcome to TRS

Just FYI the dash switches never break unless you hit them with a hammer, and very hard, lol, so always assume that part works

The 1994 and earlier controllers were also pretty bullet proof but it is 25+ year old electronics, still not the first place to look
When you press the white button LED should flash if its OK, if it stays on, no flash, then module is most likely bad, no LED means no 12volts.

The Shift motor are what wears out, or more accurately, "wears in", they fail from LACK OF USE, they sit for 11 months a year, so the electric motor brushes get rusted out and can't transfer electricity to the rotor
So close to the First thing to check

The very first thing to check are the Fuses, one in the engine bay and one in the cab fuse box

In 1989, check the 20 amp fuse in engine bay fuse box, don't have a number for 1989, this is the 12volt for the shift motor

Maybe fuse 17 in the cab, 15 amp fuse, thats for the controller

You can pull out the shift motor and test it using the battery
If there is a Brown wire attached, cut it and then splice it back together after testing, its for electric clutch in transfer case, FYI, not an integral part of the system

There is a yellow and orange wire that runs to the electric motor part, those are the 12v and ground wires
when one wire has 12v and the other ground then motor turns clockwise, if you reverse 12v and ground, then motor turns counter-clockwise
So same as a power window motor

It does have mechanical Stops, so will only turn so far one way or the other way

The other 5 wires on the shift motor are for the sensor, one has power and the other 4 will send that power back to controller as the contact wheel inside the shift motor turns, this is how the controller "knows" when shift motor is in the correct position, 2WD, 4H or 4L

 

[Fryesvan]

I’m missing a fuse in the engine bay. No 20 amp. Could that be it?

 

[RonD]

No, it looks like the 40 amp fuse is for ELEC SHIFT, test it
2nd from right