I'm thinking ths is your issue:

Subject: ABS Red Brake SVC And 4WD Light On HVAC Blower Inoperative - keywords B1375 C0379 DTC HI4 ignition IPC L04 MIL on U1000 U1041 PIT3832C (12/04/2007)

Models: 2004-2007 Buick Rainier, 2002-2008 Chevrolet Trailblazer models, 2002-2008 GMC Envoy models, 2002-2004 Oldsmobile Bravada

This PI was superseded to update Recommendation/Instructions and model years. Please discard PIT3832B.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s).

Condition/Concern:
Vehicle may exhibit a combination or all of the following symptoms: ABS light on, Red BRAKE light on, Service 4WD light on, HVAC blower motor inoperative. Various DTCs may also be present.

Recommendation/Instructions:
Diagnose for loss of battery voltage to the rear fuse block on circuit 300 ORN for the following fuses:

Note: Prior to proceeding forward with the information below, it is important to verify the voltage as indicated however it is equally important to verify the integrity of each circuit. This can be achieved by performing a voltage drop test or by adding a device to each circuit that will supply sufficient load to verify the circuits integrity.

HVAC 30A, 4WD 15A, HVAC 1 10A, BRAKE 10A, TBC RUN 3A.

1. Check circuit 300 ORN for battery voltage when the ignition key is in the RUN position.
2. Check for battery voltage at the rear fuse block under the rear seat Connector C1 pin D9.
3. If battery voltage IS NOT present at these locations, check for voltage at the ignition switch pin G for circuit 300 ORN.
4. If battery voltage IS present at the ignition switch pin G, check circuit 300 for an open.
5. If battery voltage IS NOT present at the ignition switch pin G, replace the ignition switch. Note: This PI does not apply to the Saab 97x. The 97x has a unique ignition switch location and an electrical harness. With this new switch, the electrical center pin designations and the ignition switch connector is different. In the event the concern above is experienced in a Saab 97x, circuit 300 can be checked for integrity using the appropriate schematics in eSI. Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.