Blower motor does not work at any speed

Based on the detailed information you've provided, it seems that you've done a thorough job of testing the major components related to the blower motor system in your 1999 Chevy Tahoe.
Here are a few possibilities and additional steps to consider:

High Resistance in the Circuit: Even though the wiring and connectors appear to be in good condition, there might be high resistance somewhere in the circuit that only becomes significant under load. This could be due to a partially broken wire, a corroded connector, or a faulty switch. Carefully inspect the wiring harness for any signs of damage, wear, or heat exposure.

Issue with the Control Switch or HVAC Control Unit: The problem might be with the control switch or the HVAC control unit in the dashboard. These components can sometimes develop internal faults that are not immediately apparent. Consider testing the switch and control unit if possible.

Ground Connection Problem: A poor ground connection can cause voltage drop issues. Make sure the ground connections related to the blower motor circuit are clean, tight, and free of corrosion. This includes not just the ground for the blower motor, but any related grounds in the HVAC system.

Voltage Drop Test: Perform a voltage drop test on the blower motor circuit. This test is done by measuring the voltage across different parts of the circuit while the circuit is under load. A significant voltage drop across any specific part of the circuit would indicate where the resistance problem lies.

Check for Overloading or Short Circuits: There could be an issue elsewhere in the electrical system that's causing an overload or short circuit when the blower motor is connected. This might be difficult to diagnose without specialized equipment.

Do you have power and ground at the motor ?
And what is the make model and year ?

The motor has to have voltage and a good ground.
Could be a faulty ground connection.

JUST REPLACE IT.ITS ABOUT 80.00 NEW AND 60 AT THAT JUNK YARD.

Start by checking the fuse. If the fuse is good, then either the blower motor is bad or the blower motor resistor pack is bad especially if this problem started with the lose of some of the speeds as in it only worked on high. It can be the speed control itself is bad but rarely does it go bad. You can check the motor by applying 12 volts directly to the motor to see if it is good.

The blower motor fuse,or relay is not working,check these,and the blower motor switch.The relay is activated by connecting ground to the relay.Best bet,is the blown fuse.

blower control modular,

check fuse and relay.if all is good.check blower motor to see if its getting power if so motor dont run. replace motor.if not.and fuse and relay is good.problem could be the control switch or loose broken wire at control switch.

Check the blower motor fuse to see if it is blown,and look for a blower motor relay,and check it to see if it is good.Then if you must,run a hot wire from a 12 volt power source to see if the blower will run,if not .or if it runs slow ,replace it.If the fan runs good,look at the blower control switch to be bad,replace it.

Replace your resistor if you haven't already. I had the same issue with mine, it only worked on high.