Blower Relay/Switch Location

JDL is referring to an Auto Temp Control system. If you have a manual system, the high blower relay is built into the blower resister which takes the place of the module he refers to and fails quite often. That is located under the dash on the passenger side, next to the blower motor

Here is a guide that will help

https://www.2carpros.com/articles/blower-fan-motor-works-on-high-speed-only

Check out the diagrams (Below)

Please let us know what happens.

Cheers

Thank you Wrenchtech for your replies!

I do have a manual system, and have already replaced the resistor, however the behavior did not change after this part was replaced; none of the blower speeds work at all. Is it safe to assume that the blower motor itself should be replaced?

Run power and ground directly to it to test. It sounds like the blower motor is bad.