Testing the blower motor on your 1996-2000 3.8L V6 Ford Mustang is not hard since it basically involves two simple tests.
The first one is an amperage draw test done with a multimeter in Ohms mode and the other is applying power and ground directly to the blower motor (to see if it runs).
In this tutorial I'll explain them both so that you can find out if it's defective or not.
Contents of this tutorial at a glance:
You can find this tutorial in Spanish here: Cómo Probar El Motor Del Soplador (1996-2000 3.8L Ford Mustang) (at: autotecnico-online.com).
NOTE: You can find the 1996-1998 3.8L Ford Mustang blower motor circuit diagram here: Blower Motor Wiring Diagram (1996-1998 3.8L Mustang).
The 1999-2000 3.8L Ford Mustang blower motor circuit diagram can be found here: Blower Motor Wiring Diagram (1999-2000 3.8L Mustang).
Blower Motor Basics
The blower motor, on your 3.8L Ford Mustang, is located underneath the right side (passenger side) of the dash.
As you're probably already aware, its connector has two wires coming out of it. Without going into too much detail, one wire is a power wire and the other wire is a ground wire. Since it's a two wire electrical component, testing it is a breeze.
Now, when the blower motor fails in your Ford Mustang, you're gonna' see one of the following symptoms:
- The blower motor will stop working completely.
- The blower motor will run, but run with a lot of bearing noise.
A blower motor with worn out bearings will use an extreme amount of current (from the mechanical resistance to the motor rotation). This high amperage draw can overheat and destroy the blower motor resistor and/or the blower switch.
TEST 1: Testing The Amperage Draw Of The Blower Motor
The very first thing that we're gonna' do is to test the amperage draw of the blower motor.
This is a very simple and easy test to do and will let you know if the blower motor is defective (or not) right off the bat.
This test is especially important in situations where the blower motor is running, but it's running with a lot of bearing noise or the blower motor fuse keeps getting blown.
In a few words, the amperage draw test simply involves testing the resistance of the blower motor and then using Ohm's Law to calculate it's amperage draw (Ohms Law: Amps=Volts ÷ Ohms).
NOTE: If you don't have a multimeter and need to buy one, check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing.
Let's get started:
Disconnect the blower motor from its electrical connector.
Place your multimeter in Ohms mode.
Measure the resistance of the blower motor with your multimeter. You'll be testing across the blower motor's connector and not the vehicle's wiring harness connector.
Divide 12.5 by the resistance value you got in step 3 (12.5 is the battery voltage value). The result of this calculation is the amount of amperage the fan motor is using.
To be a little more specific: Let's say that the resistance reading was .4 Ohms. This is what the math would look like: 12.5 ÷ .4 = 31.25 and this would translate to 31.25 Amps.
Let's take a look at your test results:
CASE 1: Your test result resulted in a calculation of under 30 Amps. This is the correct and expected test result and let's you know that the blower motor amperage draw is within specification.
The next step is to manually apply power and ground to the blower motor itself. For this test go to: TEST 2: Applying Power And Ground To The Blower Motor.
CASE 2: Your test result resulted in a calculation of 30 Amps or more. This test result tells you that the blower motor, on your Ford Mustang, is defective and needs to be replaced.