ALTERNATOR TEST 2: Checking for a Blown Mega Fuse
All of the electrical power that the alternator produces, to charge the battery and to power any of your Ford's electrical needs, passes thru' a single 80 or 100 Amp fuse! If this fuse is blown... the alternator could be working, but its output will never reach the battery or any accessory in or on the car that needs a steady voltage and amperage value.
So in this test step, you're going to verify that this fuse is OK on your Ford Escort (or Focus, Tracer, or 1.9L or 2.0L Ford vehicle). This is what you'll need to do:
The very first thing you need to do is to disconnect the negative battery cable terminal from the battery negative post. This is very important. Don't continue to the next step without first doing this.
After disconnecting the negative battery cable, turn on your multimeter and select Ohms mode.
Your Ford's alternator has only one big wire attached to it. This wire is attached with a nut. So, place your multimeter's RED test lead on the stud to which this wire is connected to. The arrow in the photo points to this stud.
With the BLACK multimeter test lead... probe the center of the battery positive post on your Ford's battery.
You'll get one of two results:
1.) If the 80 (or 100) Amp fuse, protecting this circuit, is blown... your multimeter will indicate a reading of OL (which means over limit).
2.) If the Inline Fusible Link (or fuse) is OK and not blown, your multimeter will register an Ohms reading of .5 Ohms or less.
OK, now that the testing part is done... let's take a look at what your results mean:
CASE 1: Your multimeter registered .5 Ohms: This is good, since it indicates that the fuse protecting this circuit is OK and not blown.
If your Ford car is a Focus, an Escort, a Tracer... you can stop here and declare the alternator as BAD and replace it.
If your car is a Contour, a Mystique or a Cougar, then I sugges one last test. This last test to do also involves checking the condition of another fuse that's also located in the Engine Compartment Fuse Box. OK, for this test, go to TEST 3.
CASE 2: Your multimeter DID NOT register .5 Ohms, it registered OL: This result tells you that the fuse is blown and this will keep the alternator from charging the battery.
Replace the fuse and retest. Replacing the fuse should solve your No Charge Condition. You'll have to investigate the reason this Inline Fusible Link or fuse blew, since they don't go BAD for no particular reason.
You're probably wondering: So where's this 80 (or 100) amp fuse located at? Well, you'll need to consult your owner's manual (or a repair manual or a Google Search), but this fuse is always located in the Under Hood Fuse Box in the engine compartment.
This step test applies to Ford Contour and Mercury Mystique and Cougar only: Your Ford Contour or Mercury Mystique will have a dedicated alternator fuse that provides the Voltage Regulator on the alternator with 12 Volts which are needed so that the alternator will start charging the vehicle's battery.
This fuse is usually a 7.5 amp plastic blade type fuse and is located in the Engine Compartment Fuse Box. You may need to consult with your Owner's Manual once again if the fuses are not labeled.
Reconnect the battery to its negative battery cable, that you disconnected in the previous test.
Locate the alternator fuse, which will be located in the fuse box in the engine compartment.
Once you have located the fuse, remove it and check that it's not blown.
If it is blown, replace it with a new one and repeat TEST 1.
CASE 1: The fuse is NOT blown This is good and let's you know that the alternator has all of the power sources it needs to charge, since it isn't... this result also let's you know that the alternator is BAD and needs to be replaced.
CASE 2: The fuse IS blown, then please replace the fuse with another of the same amperage rating and start the car and check to see if the alternator is now charging the battery by repeating TEST 1.