Test to Check Blower Switch?

88XJ, 4.0L. My blower motor stopped working after I finished installing a new stereo head unit. It does not function at any speed (not a vacuum leak causing the blower to default to high speed). The 25 amp under dash fuze is fine. I disconnected the blower motor under the hood and ran jumpered it directly to the battery and the motor fired right up. I'm assuming I may have a bad blower switch, but was wondering if anyone knows of a way to function test it to see if its good (everything appears to be in working order)?

Of course, this happens just as the cold weather moves in (9 degrees a couple mornings ago).

This is VERY common. I install 12v systems for a living and have seen it alot. There is a connection on the ac controls that tends to get knocked loose during a head unit install.It gets knocked loose when the radio is shoved back in the dash, it snagges on the wires pulling the connector apart. Just take it apart and plug it back in, being careful not to knock it off again during re-assembly.

Which electrical connector - the one to the switch, or the one that controls the air flow to the vents? Does one affect the other?

I did disconnect/re-connect the blower switch plug. I actually removed the switch and did a visual inspection of the switch contact (as much as can be seen though the small hole on the side) as I moved the switch between low and high speeds. Between the switch and connections, everything appears to be in working order. I did not inspect the air flow directional control electrical connector, as it is hard to get to and I could hear the dampers moving when switching between the vent, heat, and defrost positions.

By chance, have you ever known a radio install to pinch or short a wiring harness? The OEM radio (AM/FM only) was much shorter than the replacement unit, so there isn't a lot of room for the harnesses.

It is the black connector on top of the controls. It is the "airflow direction" electrical connector, not the actual blower speed switch. It can be attached enough to operate the airflow direction, but loose enough to prevent the fan from working. It controls the on/off for the blower, the other switch just contrrols the speed.

There is a possibility of shorting a wire, but it would most likely be the constant power for the radio/dome lights.

BINGO! Thanks Trailready. I didn't even see that connector. I had seen the wires running to the back of the air flow housing, but had not seen where I had knocked the black connector from the top of it. Once I pulled both the radio and HVAC control panel again, it stuck right out. By the looks of the connector, this probably wasn't the first time that it had been knocked about. I now have the fan back. I'm glad I mentioned the radio install in my original post. Thanks again.