How To Test The Starter Motor (1995-1998 3.8L V6 Ford Mustang)

If your 3.8L V6 Ford Mustang is suffering a 'does not crank condition', then there's a good chance that the starter motor is defective. Thankfully, testing the starter motor isn't that hard.

In this tutorial, I'll explain how to do it in a step-by-step way. You'll be able to find out if it's defective and behind the 'no-crank' problem or not.

You can find this tutorial in Spanish here: Cómo Probar El Motor De Arranque (1995-1998 3.8L Ford Mustang) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

• 3.8L V6 Ford Mustang: 1995, 1996, 1997, 1998.

STARTER MOTOR CIRCUIT WIRING DIAGRAM: You can find the wiring diagrams for the 1995-1998 3.8L V6 Ford Mustang starter motor circuit here:

• Starter Motor Wiring Diagram (1995 3.8L V6 Ford Mustang).
• Starter Motor Wiring Diagram (1996-1998 3.8L V6 Ford Mustang).

Important Safety Tips And Precautions

TIP 1: The starter motor test described in this tutorial ears and on car test. You don't have to remove the starter motor from your Ford Mustang to tested.

If you have removed it, no problem. The following tutorial will help you to bench test it: How To Bench Test A Starter Motor (Step By Step).

TIP 2: It's important that the battery, in your 3.8L Ford Mustang be fully charged. Testing the starter motor with a less than fully charged battery will give you an untrustworthy test result (that could make you end up buying parts your Mustang doesn't need).

You also need to make sure that the battery cable terminals and battery post are clean and free of corrosion.

TIP 3: If your Ford Mustang has a standard transmission, make sure that it's out of gear and in neutral, and that the parking brake is activated/on.

TIP 4: You'll need to raise your Ford Mustang to access the starter motor. Use jack stands to keep it up. Don't trust the jack!

Symptoms Of A Bad Starter Motor

The most common symptom, that you'll see when the starter motor is bad, is the engine does not turn over when you turn the key to crank and start your Ford Mustang's 3.8L V6 engine.

The starter motor can also fail intermittently, which means that it will start the car most or some of the time and then it won't.

Here's a basic list of symptoms you see when the starter motor has failed completely:

1. Jump starting the engine doesn't make it crank over.
2. The battery has been charged and/or replaced and still your Ford Mustang does not crank.
3. When you turn the key to crank the engine, all you hear is a small knock and nothing else.

Tools Needed To Test The Starter Motor

Testing the starter motor does require some basic tools. The cool thing is that they aren't expensive. Here's a basic list of what you'll need:

1. Remote starter switch.
   • If you'd like to see what a remote starter switch looks like, you can follow this link (and buy it here too): Innova 3630 Remote Starter Switch (Amazon affiliate link).
   • You can either buy this tool online or you can buy it at your local auto parts store (AutoZone or O'Reilly Auto Parts, etc.).
2. Multimeter or a 12 Volt automotive test light.
   • If you don't have a multimeter or need to upgrade yours, check out my recommendation here: Tekpower TP8268 AC/DC Auto/Manual Range Digital Multimeter (Amazon affiliate link).
3. A wire piercing probe.
   • This tool is not an 'absolute must-have tool' but I can tell you from experience that it makes it a whole lot easier to probe the S terminal wire for the start signal.
   • If you'd like to see what this tool looks like, you find out more about it here: Wire Piercing Probe Tool Review (Power Probe PWPPPPP01).
4. A helper.

As you can see, you don't need anything expensive. OK, let's turn the page and get starter with the first starter motor test.

Starter Motor Solenoid S Terminal Info

There are 2 types of starter motors that are used on the 3.8L V6 Ford Mustang. The main difference lies in how the S terminal wire is attached to the starter solenoid.

TYPE 1: The factory original starter motor has the S terminal wire connecting to a male spade terminal on the starter solenoid.

On this type, the S terminal wire has a female quick disconnect type connector.

TYPE 2: On the after-market starter motors, the S terminal wire connects to a threaded stud and a nut fastens it in place.

On this type, the S terminal wire has a circular (ring) connector. To remove this connector, you have to remove the nut that locks/fastens it in place.

Both type of starter motors work in the exact same way and are pretty much tested in the same way too.

TEST 1: Applying 12 Volts To The Starter Motor S Terminal

The 1st order of business, when testing the starter motor, is to bypass the ignition switch and directly apply power to the starter motor solenoid's S terminal to see if the starter motor cranks the engine.

If when applying battery power directly to the starter motor and it cranks the engine, then you can eliminate the starter motor itself has the defective.

I can tell you from personal experience, that the fastest, easiest, and safest way to apply battery power to the starter motor is by using a remote start switch. You can see an example of this tool (and where to buy it) here: Innova 3630 Remote Starter Switch (Amazon affiliate link).

Now, if the starter motor doesn't turn the engine over, when applying battery power to it with the remote start switch, then you can conclude that the starter motor itself is defective or that it's not getting enough current from the battery because of a voltage drop on the battery cable (we'll test this in TEST 3).

IMPORTANT: Before you perform this test remove the key from the ignition switch to prevent the engine from accidentally starting. If your Ford Mustang is equipped with a standard transmission, place it in neutral.

IMPORTANT: Place your Ford Mustang on jack stands if you raise it to access the starter motor!

OK, these are the test steps:

1. 1

   Disconnect the battery negative (-) terminal.
   
   You'll reconnect it back in one of the following steps, for now, it's a safety precaution as you set up the test.

2. 2

   Attach one of the alligator-type terminals of the remote starter switch to the S terminal of the starter motor.
   
   If the S terminal wire has a female quick disconnect connector, you can disconnect the wire from the starter solenoid and connect the remote start switch connector directly on the solenoid's male spade terminal.
   
   If the S terminal wire has a ring type connector (and is fastened by a nut to the stud), don't disconnect it from the starter solenoid. You can connect the remote start switch connector onto the stud with the wire still connected to it.

3. 3

   Reconnect the negative (-) battery cable to the battery negative (-) post.
   
   NOTE: Make sure that the battery cables and posts are clean.

4. 4

   Connect the remaining alligator-type terminal of the remote starter switch to the battery positive (+) post.
   
   IMPORTANT: If your Ford Mustang has a standard transmission, make sure it's out of gear before you make this last connection.

5. 5

   Activate the starter motor with your remote starter switch. As you apply these 12 Volts (to the S terminal of the starter motor), you'll get one of two results:
   
   1) The starter will activate and will turn over the engine -OR- 2) The starter motor won't do a thing.

Let's examine your test result:

CASE 1: The starter motor cranked the engine. This test result lets you know that your Ford Mustang's starter motor is OK and functioning.

If the starter motor is NOT cranking the engine when you turn the key to start it, then it's probably not receiving the activation signal from the ignition switch.

To further test this, go to the next test: TEST 2: Verifying The Start Signal.

CASE 2: The starter motor DID NOT crank the engine. This usually means that your Ford Mustang's starter motor is bad and needs to be rebuilt or replaced.

I suggest 2 more tests and these are make sure that the starter motor is getting its 12 Volt signal signal and to test the battery cable (that attaches to the starter motor solenoid) for corrosion. This can be accomplished very easily with a voltage drop test.

• Go to: TEST 2: Verifying The Start Signal.
• Go to: TEST 3: Voltage Drop Testing The Battery (+) Cable.

If the above two tests confirm that the start signal IS present and there's no voltage drop on the battery cable (feeding battery power to the starter motor), then you can confidently conclude your Ford Mustang's starter motor is bad and needs to be replaced.

TEST 2: Verifying The Start Signal

You've reached this point because the starter motor on your Ford Mustang cranked the engine when you applied battery powered directly to the S terminal of the starter solenoid.

In this test step, we're gonna' make sure that the start signal is present in the S wire that connects to the S terminal of the starter solenoid.

This is a very simple test and it's done with a multimeter in Volts DC and simply involves making sure that when you turn the key to crank and start the engine, battery voltage is present on the wire that connects to the S terminal of the starter solenoid.

OK, these are the test steps:

1. 1

   Connect the red multimeter test lead to the S terminal of the starter motor.
   
   If the S wire has a female quick disconnect connector, disconnect the wire from the solenoid and connect the red multimeter test lead to the connector on the wire itself.
   
   If the S wire has a ring type connector and is fastened to the stud via a nut, then connect the red multimeter test lead to the S terminal stud (without removing the S wire from the stud).

2. 2

   Attach the black multimeter test lead to a clean and rust-free spot on the engine or on the vehicle frame.
   
   I recommend that you use a battery jump start cable to Ground the black multimeter test lead directly to the battery negative (-) terminal.

3. 3

   Have your helper crank the engine from inside your Ford Mustang.
   
   The engine won't turn over, but the idea is to verify that the starter motor's internal solenoid is getting the 12 Volt start signal from the ignition switch (or not).

4. 4

   Your multimeter is going to register one of two results: Either 9 - 12 Volts DC or no voltage at all.

Let's analyze your test result:

CASE 1: The multimeter registered 10 to 12 Volts. This is the correct test result and tells you that the starter motor is receiving its activation signal.

This test result eliminates the safety neutral switch and the ignition switch as being faulty. The next step is to do a voltage drop test on the starter's battery cable. For this test go to: TEST 3: Voltage Drop Testing The Battery (+) Cable.

CASE 2: Your multimeter DID NOT register 10 to 12 Volts. This result tells you that the starter motor is not getting its activation signal. Without it, the starter motor will not crank the engine when you turn the key to crank and start the engine.

Usually, when the starter's activation signal is not present on the wire that connects to the starter solenoid's S terminal, it's usually because:

• The ignition switch is faulty.
• The starter relay is defective.
• The neutral safety switch is faulty or misaligned.

Although it's beyond the scope of this article to test the neutral safety switch, the starter relay, or the ignition switch, you have eliminated the starter motor as defective. The following wiring diagram will help you track the problem down:

• Starter Motor Wiring Diagram (1996 3.8L V6 Ford Mustang).
• Starter Motor Wiring Diagram (1996-1998 3.8L V6 Ford Mustang).

TEST 3: Voltage Drop Testing The Battery (+) Cable

If you've reached this point, you have confirmed that:

• The battery is fully charged.
• The starter motor is getting a 'start' signal (TEST 2) when you turn the key to crank the engine but the starter motor does not crank your Ford Mustang's engine.

In this test, we're gonna' make sure that the starter motor is receiving the full amount of current it needs from the battery.

In some cases the starter motor, although in perfect working condition, does not crank the engine because it does not receive the full amount of current that the battery provides.

This is usually due to some sort of hidden corrosion on the battery cable that connects the starter motor to the battery.

By doing a simple multimeter voltage drop test, you can find out if this is the case.

Let's get testing:

1. 1

   Place your multimeter in Volts DC mode.

2. 2

   Attach the black multimeter test lead to the center of the positive (+) battery terminal.
   
   If the positive battery post isn't clean, clean a spot right on the top of it. It's important that the multimeter lead make contact right in the center of the positive battery post.

3. 3

   Connect the black multimeter test lead to the center of the stud to which the big battery cable attaches to on the starter solenoid.

4. 4

   Have your helper crank the engine even though the starter motor isn't cranking the engine.
   
   This is important, since a voltage drop test has to be done while the component in question is working (or trying to work).

5. 5

   If all is good (no voltage drop), your multimeter will register 0 Volts (.5 Volts is still 0 Volts).
   
   If there's a voltage drop (which is bad), your multimeter will register voltage (usually above 5 Volts DC).

Let's take a look at what your results mean:

CASE 1: Your multimeter registered 0 Volts (no voltage drop). This is the correct test result and tells you that the starter motor is receiving all of the battery voltage and amperage it needs to crank the your Ford Mustang's engine.

You can conclude your Ford Mustang's starter motor is defective if you have:

• Confirmed that the starter motor doesn't work when you apply power to the S terminal wire of the starter motor (TEST 1).
• Confirmed that the starter motor is receiving the crank signal (TEST 2).
• In this test step, you have confirmed that no voltage drop exists on the battery positive cable.

Replacing the starter motor should solve your no-crank condition.

I'm going to make two more recommendations to you:

• Before removing the starter motor, manually turn the engine using a 1/2 ratchet and the appropriate socket. This is to make sure that the engine or the A/C compressor have not locked up and causing the no-crank condition.
• Bench test the starter motor after removing it. This is a super easy test to do and this tutorial will help: How To Bench Test A Starter Motor (Step By Step).

CASE 2: Your multimeter registered 5 Volts or more. This result tells you that a voltage drop does exist and that the battery's full power is not reaching the starter motor.

The good news is that this can easily be corrected, since a voltage drop is always caused by some sort of corrosion issue on the battery positive cable or terminals or the battery positive (+) post.

The solution is to thoroughly clean the battery positive (+) post and the battery positive (+) terminal (both the end that attaches to the battery positive (+) post and the end the connects to the starter motor's battery (+) cable stud.

After cleaning, try cranking the engine. If it cranks and starts, no further testing is required.

More 3.8L V6 Ford Mustang Tutorials

You can find a complete list of 3.8L V6 Ford Mustang tutorials in this index:

• Ford 3.8L Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

• How To Test The Fuel Injectors (1994-1995 3.8L Ford Mustang).
• Constant Control Relay Module (CCRM) Circuits (1996-1997 3.8L Ford Mustang).
• How To Test The TPS With A Multimeter (1994-1995 3.8L Mustang).
• How To Test The Radiator Fan Motor (1997-1999 3.8L Ford Mustang).