4 wheel drive not working!

I have mentioned this so many times. Drive your Taco in 4 Hi once a month for at least 10 miles or so to keep everything lubricated or it will fail you.

 

In that case, I would first make 100% sure that the truck is actually fully in 2hi (jack up front wheels if you need to.)
[Check that the front ADD is disconnected (front wheels don't differential) and also that the transfer case is in 2hi (check that the front driveshaft is free).]

Next disconnect the ADD actuator at its connector and the Transfer actuator at their connectors.
Then at the ADD and Transfer actuators, check that the feedback matches acceptable values
4WD Actuator Troubleshooting (Transfer Case and ADD) | Tacoma World
(DL1, DL2, and ADD signals to ground pin for ADD Actuator)
(TL1, TL2, TL3, 4WD, and L4 signals to ground pin for the Transfer Actuator)

Also check the resistance of the motor in each (DM1 to DM2 and TM1 to TM2), but it does not sound like that is the issue.

Based on your description, I think it is VERY likely that you will find that either the Transfer Actuator or ADD Actuator will not have the correct feedback signals (or a wire is obviously damaged going to one or the other). Based on anecdotal evidence in addition to your symptoms, statistically it will be the ADD wipers.

Let us know what the results are in this thread.
Good Luck