This 1993 Honda Civic came in with the complaint that the blower motor does not work on any speed. The blower motor is located under the passenger side of the dash. I depressed the thumb latch and pulled the connector from the blower motor.
I checked power on both wires and nothing was there. key was on and the blower switch was set to high.
There should have been power on the blue/white wire. The blue/black wire is the ground control wire. It feeds through the blower switch and blower resistor.
I looked at my wiring diagrams and discovered there was a blower relay in the underhood fuse box. That fuse box is located under the hood on the passenger side of the vehicle.
The blower relay is located in the top center of the picture below.
The blower relay.
I am using a simple test light for the following tests because I had already checked the wiring diagrams and determined it was safe for a testing. On many systems a test light cannot be used due to possible damage to electronic modules. Ignition power from the interior fuse box.
Constant power from the blower fuse that is located just below the relay.
Notice in the next pictures that my test light lead is attached to battery positive. When the tip of the light is touched to ground the bulb will light up. In this case I am checking a return ground from the blower motor.
Constant ground for the relay coil.
I jumped the terminals from blower fuse to the blower motor. The blower worked. Please keep this one fact in mind. I know exactly what is on the other end of a terminal before I jump a circuit. One wrong move and you can cost yourself thousands in repairs. I had already looked at wiring diagrams and had determined that there were no electronic modules of any kind connected to these four terminals.
Just in case someone needs to know the ignition feed fuse in the interior fuse box. Fuse #13.
The new relay on the left and the old one on then right. There are clips on both sides that hold the relay in place. Kind of a pain to release. If you just pull firmly and wiggle the relay it will release. One of the clips will generally break in doing so though.
You may also notice that there are three relays in the underhood fuse box that all have the same part number. If you want you can take the one out for the rear window defogger to test with.