Ken
Gone but not forgotten
In response to a question from another thread, I'll start a new one instead of hijacking the other. I can't remember how to make tables in this forum so what you see is what you get. 
Straight from the Helm GM Electrical Diagnosis Service Manual Supplement:
COOLANT FAN TROUBLESHOOTING HINTS
Try the following checks before doing the System Check:
Action: With the ambient temperature above 60° and the engine cold and idling, move A/C Function Selector to NORM (if equipped with A/C).
Normal Result: Coolant fan should start after a short period.
Action: Move A/C Function Selector to OFF.
Normal Result: Coolant fan turns off.
Action: With the engine warmed up, run it for at a fast idle for several minutes.
Normal Result: Coolant fan turns on before Auxiliary Coolant Fan (if equipped) and before Coolant Temperature Indicator comes on.
AUXILIARY COOLANT FAN DOES NOT TURN ON (Table 1)
Connect: FUSED JUMPER
At: COOLANT FAN TEMPERATURE SWITCH CONNECTOR (Disconnected)
Condition: Ignition Switch: RUN
Connect between: DK GRN/WHT & Ground
Correct Result: Auxiliary Coolant Fan runs.
For Diagnosis: Leave fused jumper connected and go to Table 2.
* If fan runs, replace Coolant Fan Temperature switch.
AUXILIARY COOLANT FAN DOES NOT TURN ON (Table 2)
Connect: TEST LAMP
At: AUXILIARY COOLANT FAN RELAY CONNECTOR (Disconnected)
Conditions: Ignition Switch: RUN, Fused Jumper from Table 1 still in place.
Connect Between: C (DK BLU) & Ground
Correct Result: Lamp lights.
For Diagnosis: Check C. FAN Fuse and DK BLU (351) wire for an open.
Connect Between: C (DK BLU) & B (DK GRN/WHT)
Correct Result: Lamp lights.
For Diagnosis: Check DK GRN/WHT (335) wire for an open.
Connect Between: E (RED) & Ground
Correct Result: Lamp lights.
For Diagnosis: Check Fusible Link E and RED (2) wire for an open.
* If all above results are correct, go to Table 3.
AUXILIARY COOLANT FAN DOES NOT TURN ON (Table 3)
Connect: 20 AMP FUSED JUMPER
At: AUXILIARY COOLANT FAN RELAY CONNECTOR (Disconnected)
Connect Between: E (RED) & A (BLK/RED)
Correct Result: Auxiliary Coolant Fan runs.
For Diagnosis: Leave Fused Jumper connected and go to Table 4.
* If result is correct, replace the Auxiliary Coolant Fan Relay.
AUXILIARY COOLANT FAN DOES NOT TURN ON (Table 4)
Connect: TEST LAMP
At: AUXILIARY COOLANT FAN MOTOR CONNECTOR (Disconnected)
Condition: Fused Jumper from Table 3 still in place.
Connect Between: B (BLK/RED) & Ground
Correct Result: Lamp lights.
For Diagnosis: Check BLK/RED (903) wire for an open.
Connect Between: B (BLK/RED) & A (BLK)
Correct Result: Lamp lights.
For Diagnosis: Check BLK (151) wire for an open.
* If result is correct, replace the Auxiliary Coolant Fan Motor.
Straight from the Helm GM Electrical Diagnosis Service Manual Supplement:
COOLANT FAN TROUBLESHOOTING HINTS
Try the following checks before doing the System Check:
- Visually check the C. FAN fuse.
- If the Coolant Fan runs with the Ignition Switch off, replace the Coolant Fan Relay.
- If the Auxiliary Coolant Fan runs with the Igniton Switch off, replace the Auxiliary Coolant Fan Relay.
Action: With the ambient temperature above 60° and the engine cold and idling, move A/C Function Selector to NORM (if equipped with A/C).
Normal Result: Coolant fan should start after a short period.
Action: Move A/C Function Selector to OFF.
Normal Result: Coolant fan turns off.
Action: With the engine warmed up, run it for at a fast idle for several minutes.
Normal Result: Coolant fan turns on before Auxiliary Coolant Fan (if equipped) and before Coolant Temperature Indicator comes on.
AUXILIARY COOLANT FAN DOES NOT TURN ON (Table 1)
Connect: FUSED JUMPER
At: COOLANT FAN TEMPERATURE SWITCH CONNECTOR (Disconnected)
Condition: Ignition Switch: RUN
Connect between: DK GRN/WHT & Ground
Correct Result: Auxiliary Coolant Fan runs.
For Diagnosis: Leave fused jumper connected and go to Table 2.
* If fan runs, replace Coolant Fan Temperature switch.
AUXILIARY COOLANT FAN DOES NOT TURN ON (Table 2)
Connect: TEST LAMP
At: AUXILIARY COOLANT FAN RELAY CONNECTOR (Disconnected)
Conditions: Ignition Switch: RUN, Fused Jumper from Table 1 still in place.
Connect Between: C (DK BLU) & Ground
Correct Result: Lamp lights.
For Diagnosis: Check C. FAN Fuse and DK BLU (351) wire for an open.
Connect Between: C (DK BLU) & B (DK GRN/WHT)
Correct Result: Lamp lights.
For Diagnosis: Check DK GRN/WHT (335) wire for an open.
Connect Between: E (RED) & Ground
Correct Result: Lamp lights.
For Diagnosis: Check Fusible Link E and RED (2) wire for an open.
* If all above results are correct, go to Table 3.
AUXILIARY COOLANT FAN DOES NOT TURN ON (Table 3)
Connect: 20 AMP FUSED JUMPER
At: AUXILIARY COOLANT FAN RELAY CONNECTOR (Disconnected)
Connect Between: E (RED) & A (BLK/RED)
Correct Result: Auxiliary Coolant Fan runs.
For Diagnosis: Leave Fused Jumper connected and go to Table 4.
* If result is correct, replace the Auxiliary Coolant Fan Relay.
AUXILIARY COOLANT FAN DOES NOT TURN ON (Table 4)
Connect: TEST LAMP
At: AUXILIARY COOLANT FAN MOTOR CONNECTOR (Disconnected)
Condition: Fused Jumper from Table 3 still in place.
Connect Between: B (BLK/RED) & Ground
Correct Result: Lamp lights.
For Diagnosis: Check BLK/RED (903) wire for an open.
Connect Between: B (BLK/RED) & A (BLK)
Correct Result: Lamp lights.
For Diagnosis: Check BLK (151) wire for an open.
* If result is correct, replace the Auxiliary Coolant Fan Motor.
