1998 w900 blower motor not working. Receiving 9v

Your blower motor is toast. You’re only seeing 9v due to the fan motor speed resistor. If the fan speed resistor fails then your fan would work by only hi speed.

 

A lot of 9’a in that post

 

Yes. The blower motor speed control is a bank of resistors. It steps the voltage down to control the motor speed. If the resistors fail the blower motor will run but only on high speed, you won’t have the lower settings. You have power to the motor and it doesn’t work, the motor is bad.

 

The Kenworth blower motor speed control switch is notorious for the rivets
that hold the terminals on coming loose. Over time resistance develops and
the motor can stop working as a result. There should be a thermal fuse in the
blower resistor that can fail as well. when the thermal fuse fails the blower
will only run on high. Also there should be a fuse in the fuse box for the heater
blower. Make sure the fuse or breaker has a good connection, I have seen a
few melted segments in KW fuse boxes.

 

Check the ground side. Voltage will be seen all the way up to an open in the circuit. If the open is on the ground side, you'll still see voltage going into the motor.

Highly doubt there's an issue on the power side since voltage is getting to the motor but I'm also not there seeing what you see either.

 

As AModelCat said, did you confirm the ground. If you checked the power with the test light grounded to the chassis you probably have a ground off. Put a pin in the ground wire and hook the light on there, no power no ground.