You can easily test the alternator on your Ford Crown Victoria or Grand Marquis with a multimeter and without having to remove it from its place on the engine.
I'll show you how in this tutorial and with your test results, you'll quickly find out if the alternator is good or if it's bad.
Contents of this tutorial:
APPLIES TO: This tutorial applies to the following vehicles:
- 4.6L Ford Crown Victoria: 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003.
- 4.6L Mercury Grand Marquis: 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003.
NOTE: On the 2003 year model, only early production vehicles.
WIRING DIAGRAMS: The alternator circuit wiring diagrams for the 1995-2003 4.6L Crown Victoria (Grand Marquis) can be found here:
- Alternator Circuit Wiring Diagram (1995-1997 4.6L Crown Victoria, Grand Marquis).
- Alternator Circuit Wiring Diagram (1998-2000 4.6L Crown Victoria, Grand Marquis).
- Alternator Circuit Wiring Diagram (2001-2002 4.6L Crown Victoria, Grand Marquis).
- Alternator Circuit Wiring Diagram (2003 4.6L Crown Victoria, Grand Marquis).
F-Series Pickups: You can find the alternator test for the F-Series pickups here:
- How To Test The Alternator (1997-2002 4.6L, 5.4L Ford F150, F250, F350) (at: easyautodiagnostics.com).
Symptoms Of A Bad Alternator
Every time you start your engine, the starter motor drains a lot of the battery's charge. Once the engine starts, the alternator starts recharging the battery so it's ready for the next engine start.
But the alternator does more than just charge the battery. It also supplies electrical power to all your vehicle's accessories, like the radio, headlights, and wipers, while the engine is running. This is important as the battery alone wouldn't able to handle this load on its own.
Eventually, the alternator will wear out and stop charging the battery. When this happens, you'll notice one or more of the following symptoms:
- The battery light on the instrument cluster lights up.
- The headlights rum dim while the engine is running and gradually get dimmer until the engine stalls.
- Your vehicle needs a jump-start every time you turn it off.
- The battery has to be recharged (with a battery charger) constantly.
Important Testing Tips
Here are a few important safety tips and testing suggestions that'll help you successfully test the alternator:
- Charge the Battery: Make sure the battery is fully charged before starting TEST 1 of this tutorial.
- Keep Hands and Tools Clear of Moving Parts: The first alternator test involves checking the battery's voltage with the engine running. Be careful of the spinning serpentine belt, pulleys, and anything that's moving on that engine. Keep your hands and tools away from these moving parts to avoid injury.
- Clean Battery Posts: Clean and remove any corrosion from the battery cable terminals and battery posts before you begin the alternator test.
TEST 1: Battery Voltage Test With Engine Running
To get our alternator diagnostic started, we're gonna check the battery voltage with the engine running.
It's super important that your Crown Vic or Grand Marquis' battery is fully charged for this test because the engine needs to run for a few minutes while you measure the battery's voltage with your multimeter.
If the alternator is functioning correctly and charging the battery, your multimeter should show a reading between 13.5 and 14.5 Volts DC.
If the alternator isn't charging the battery, you'll see a voltage reading of 12.5 Volts or less.
By the way, if you don't have a multimeter, check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing.
NOTE: You'll be working around a running engine, so be careful and take all necessary safety precautions.
OK, here's the first test:
- 1
Start the engine and let it idle.
- 2
Place your multimeter in Volts DC mode.
- 3
Check the battery's voltage with your multimeter.
- 4
The multimeter should register 13.5 to 14.5 Volts.
If it doesn't, don't worry about this just yet, continue to the next step. - 5
Turn on every accessory possible while observing the multimeter. Like the headlights, the A/C or heater (high blower speed), the windshield wipers, the radio, the rear window defroster, etc.
As each accessory comes on, they'll place a load on the charging system (alternator). - 6
The multimeter's voltage reading will decrease slightly and then stabilize around 13.5 to 14.5 Volts DC as each accessory comes on.
- 7
Let the engine run for about 5 minutes with all of the accessories on.
- 8
The battery voltage should remain between 13.5 to 14.5 Volts DC with all of the accessories on during the whole 5 minute duration.
OK, let's interpret the results of your test:
CASE 1: Your multimeter registered 13.5 to 14.5 Volts from the start of the test to the end of the test. This confirms that the alternator is working like it should. No further testing is required.
CASE 2: Your multimeter DID NOT register 13.5 to 14.5 Volts from start to end and the voltage dropped to 10 Volts or less. This test result lets you know that the alternator is probably bad.
To be 100% sure the alternator is bad, there are 2 more tests to do and I'll show you how to do them. Go to: TEST 2: Checking The Continuity Of The BAT + Circuit.
TEST 2: Checking The Continuity Of The BAT + Circuit
As you probably know, on the back of the alternator, there's a cable attached to it with a nut. This cable connects to the battery and delivers the alternator's output to it.
Before the alternator's output reaches the battery on this cable, it passes through an inline fusible link. In some cases, this fusible link gets blown. The end result is the alternator's output not being able to reach the battery.
To make sure the fusible link(s) is(are) not blown, we'll perform a simple continuity test on this circuit. The expected result of this test is for our multimeter to show continuity, which will confirm the alternator's output is reaching the battery.
NOTE: This is an on-car test. The illustration above shows the alternator removed from the vehicle only to better explain the test connections.
OK, let's get started:
- 1
Disconnect the battery negative (-) cable from the battery but leave the positive (+) cable connected to the positive (+) post.
IMPORTANT: Do not proceed to the next steps until you have done this first. - 2
Set your multimeter to Ohms mode.
- 3
Connect the red multimeter test lead to the stud shown in the photo above.
The alternator output wire connects to the stud indicated by the arrow (in the photo above).
NOTE: Don't disconnect the cable from the alternator. - 4
Connect the black multimeter test lead on the battery positive (+) terminal (at the battery).
The battery negative (-) wire must remain disconnected from the battery. - 5
Your multimeter will register one of two values:
1.) Continuity (usually an Ohms value of about 0.5 Ohms).
2.) No continuity (an infinite Ohms reading (OL)).
Let's interpret your test results:
CASE 1: Your multimeter registered continuity. This result indicates that the fusible link or fusible links are OK and not blown.
Now, there's just one more thing to check and you're done! The next test is to make sure that the alternator's voltage regulator is getting power. For this test, go to: TEST 3: Making Sure The Voltage Regulator Is Getting Power.
CASE 2: Your multimeter registered an open-circuit (OL). This result tells you that the fusible link or fusible links are blown.
Replace the fusible links and retest. More than likely your problem will be solved and the alternator will begin charging again.
Blown fusible links don't happen very often. But if it does, you'll have to find out the reason for this, since they don't get blown for no apparent reason.
You'll need to consult a repair manual to find the exact location of this fusible links. But, it's general location is in the battery cable that connects to the alternator to the battery or engine compartment fuse box. If you follow this cable to its final destination, you'll find the inline fusible links.