It only works on 4. Is this still a blower motor resistor issue?
Thanks!

 

Get out your test light and make sure that your resistor is getting juice to the required pins in the connector.

What year truck do you have?

 

Yap I would say it's a resistor problem
Depending on your truck... You may have to replace the blower motor cause the resistor is in the motor housing. Or you may get lucky and the resistor is external

 

As easy as it is to say it's the resistor, the control heads also go pretty frequently. My dad's 97 has a bad #4 position and the first thing I did is replace the resistor and I had no change.

So do some testing first to figure out where your problem is