In the truck!
Inside the blower motor housing directly behind the electrical coupler.
In the 1999 Trooper the relay is sbove the inside fuses. It is above the fuse door, so that the whole panel by bottom of the driver door must be pulled. Don't know if that helps for 1990. Note: My fuse, relay and motor are good, but no power to motor. added 1/22/2008 The blower motor resistor is located on the housing located on the firewall. This housing is were the blower motor is.
they are usually found close to the blower motor.
If you are saying that the blower motor only works on the high speed setting, then the Blower Motor Resistor is defective and needs replacing.
Check to see if you are getting power to blower motor--if so, bad blower motor If no power- perhaps bad resistor pack at blower motor Bad switch?
If you are saying the Blower Motor only works on high, then your problem is a defective Blower Motor Resistor Pack. Replace it.
Blower motor is usually behind the dash on the passenger side. Try removing the glove compartment to access it. If the blower isn't working, it could also be the resistor block (more likely to burn out than the motor itself). One blown resistor could keep the blower from blowing at all. Check that first (look for scorching and test with a test light). It's a pretty easy replacement and if the blower is not getting current replacing the motor won't do you any good.
i had a 1990 acura legend my blower motor was located under the passenger side dash board
On a 1990 LX 3.0 V-6 it is under the dashboard on the passenger side right next to the blower motor. It only has 2 screws in it. If it is malfunctioning your blower motor would still most likely work at the high speed setting.
In my '95 cherokee, the blower motor resistor is under the glove box. I assume it's about the same on a 1990. I posted instructions (with pictures, so at least you'll know what you're looking for) for replacing it on www.timsjeepblog.com.