Another thing you can do is place the ground jumper along the various yellow/red connection points to see if you can make the blower turn on. When you get to a point that has good connection to the resistors the motor will turn on.

Another thing you can do is place the ground jumper along the various yellow/red connection points to see if you can make the blower turn on. When you get to a point that has good connection to the resistors the motor will turn on.

That will work, as long as the problem isn't with the switch contacts that power the coil of the blower motor relay in the med-low (2) position. To eliminate that possibility, if using a grounded wire as Cougar suggests make sure to do the same at the green/black wire.

 

With either a voltmeter or the grounding approach, the green/black wire can be checked anywhere it's accessible. That doesn't have to be at the switch; in this particular case the test results will be the same.