4 Wheel Drive/SUVs: Please Help, model trucks, harness kit

Question
my 1996 4x4 tahoe will go into four high but not four low

Answer
Josh,
There is a bulletin out on similar problems.  Here is a copy of that bulletin.

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.
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There are several other bulletins out on the transfer case.  You can look them up on line and see if they will help diagnose your problem.

Here is a list of them:
  NUMBER          DATE
06-04-21-001         05/17/2006     Drivetrain - Updated Transfer Case Speed Sensor Conn.
05-04-21-002         03/10/2005     Drivetrain - Transfer Case Control Module Replacement
05-04-21-001         03/08/2005     Transfer Case - RTV Silicone Sealant Usage Precaution
03-04-21-003         05/01/2003     Drivetrain - Revised Transfer Case Service Procedures
99-04-21-004A         09/01/2001     Transfer Case - Bump/Clunk Update
76-43-01A         09/01/1998     Drivetrain - Slow Or No Engagement of Front Axle
86-74-04         09/01/1998     Transfer Case - Low Fluid Level/Transfer Case Overfilled
667402          03/01/1996     Transfer Case Controls - Corrected Terminal Call-out
567401          01/01/1996     Transfer Case Harness Connector - Callout Revision

As there are 4 different transfer cases used in this year Chevy, and without physically checking out the problem in person, all I can do, is to suggest possible remedies for repair.

Carl