Four wheel drive not working

It sounds like an issue with the actuator. Remove it and see if it operates or see if it is getting power when you switch to four wheel drive.

There is a bulletin for this problem I found for you File In Section: 4 Drive Axle

Bulletin No: 76-43-01A

Date: September, 1998

Subject:
Slow or no Engagement of Front Axle when 4WD is selected (Replace Front Axle Actuator)

Models:
1988-97 Chevrolet and GMC K Models
excluding 1988-93 Models over 8500 # GVW

This bulletin is being revised to add information to the Service Procedure, add a new part number, and include schematics. Please discard Corporate Bulletin Number 76-43-01 (Section 4 - Drive Axle).

Condition

Some owners may comment that the colder the outside temperature is, the longer it takes for the front axle to engage when 4 wheel drive is selected, or the front axle does not engage.

Cause

The front axle engagement actuator is a thermally activated component. Because of this characteristic, the time required for the actuator to complete 4 wheel drive engagement is extended as the temperature drops.

Correction

Replace the front axle actuator and include the applicable wiring harness kit. Refer to the Parts Information in order to determine which wiring harness kit is needed.

1996 model trucks with a build date on or after January 2, 1996 are considered as "961". If the build date of the truck is unknown, verify the 3 character "axle code" on the front axle label in order to determine which wire harness to order.

This new actuator uses a motor to engage the front axle and is not affected by temperature. On 1988-93 models with a GVW rating over 8500$, the new actuator cannot be installed and the thermal actuator will remain the service part.

Parts Information

P/N Description Qty
26060073 Actuator Asm, Frt Drive Axle 1
22510339 Fastener 1
15313272 Harness, Jumper (Z Splice) 1
(86-93 K1-3)
Parts are currently available from GMSPO.

Warranty Information

Some owners with actuators that are operating as designed (5-30 seconds engagement time) may choose to upgrade to the fast actuator at their own expense. The fast actuator is a new product enhancement and should not be used to replace actuators that are operating as designed.

Also look at the actuator in the front differential it can cause the problem as well #7

Check out the diagrams (Below)

Let us know what happens and please upload pictures or videos of the problem.

Cheers, Ken