Testing the alternator on your 1994-1998 Dodge Ram pickup, to see if it has failed (or not), can be done with a simple multimeter.
In this tutorial, I'll show you how to do it in a step-by-step fashion.
NOTE: Although you could apply the basics of this tutorial to test any alternator... you do have to check the alternator 120 amp mega-fuse in the power distribution center (located under the hood) and the illustration I'm using only apply to the 1994 to 1998 Dodge Ram pick-ups.
Contents of this tutorial:
- Symptoms Of A Bad Alternator.
- TEST 1: Battery Voltage Test With Engine Running.
- TEST 2: Checking The Continuity Of The Bat (+) Cable.
- TEST 3: Part 1 -Alternator Is New But It Still Doesn't Charge The Battery.
- TEST 3: Part 2 -Testing the Voltage Regulator Inside the PCM.
- Where To Buy The Alternator.
- More 3.9L, 5.2L, 5.9L Dodge Tutorials.
Symptoms Of A Bad Alternator
In a nutshell, your Dodge Ram pick-up's alternator has two very important jobs to do:
- Charge the battery, as the engine runs, so that you crank and start your Dodge Ram pick-up the next time you need to.
- Provide electrical current to all of the accessories while the engine runs. These accessories include:
- Blower motor (for A/C or heater).
So, when the alternator fails, you'll notice one or several of the following symptoms:
- The charge light (also known as the battery light) will be shining nice and bright on your pick-up's instrument cluster.
- Whenever you turn on the headlights (night driving), they glow very dim.
- The engine won't crank. It will only crank and start if you jump start your pick-up.
- The only way the engine cranks and starts is if you charge the battery.
- The engine stalls and won't crank (unless you jump-start it).
TEST 1: Battery Voltage Test With Engine Running
This first test will confirm that the alternator is either not charging the battery or that it is charging it.
What you'll do is measure the battery's voltage with your Dodge Ram pick-up's engine running.
If your multimeter registers 12.5 Volts (or less), then the alternator is not working and thus not charging the battery.
Now, if your multimeter registers 13.5 to 14.7 Volts with the engine running, then the alternator is working and thus charging the battery.
NOTE: You'll need to make sure that the battery has enough of a charge to keep your Dodge Ram pick-up running for at least 5 minutes to do this test. If the battery is completely dead, charge it up enough so that it can crank and start the engine.
These are the test steps:
Crank and start your Dodge pick-up and select Volts DC mode on your multimeter.
Probe the positive battery terminal with the red multimeter test lead.
With the black multimeter test lead, probe the negative battery terminal on your Dodge pick-up's battery.
Your multimeter is gonna' register one of two possible readings and they are:
1.) A steady 13.5 to 14.5 Volts DC.
2.) Or 12.5 Volts that will decrease the longer the engine stays running.
Put an electrical load on the alternator to further confirm that it's either charging or not charging.
You can do this by turning on every accessory possible (inside the vehicle). For example: Turn on the A/C or heater on high, turn on the windshield wipers, turn on the headlights, turn on everything and anything that uses electricity inside and outside of the vehicle.
Your multimeter will show you one of two things (as you turn on all of this stuff):
1.) The multimeter will register a nice and steady 13.5 to 14.5 Volts DC no matter what gets turned on.
2.) It will register 12.5 V DC and this voltage will decrease more and more as you turn on stuff inside your Dodge vehicle.
OK, let's interpret your multimeter test results:
CASE 1: Your multimeter registered 13.5 to 14.7 Volts. This test result confirms that your Dodge Ram pick-up's alternator is OK and that it is charging the battery.
If the alternator were fried, the voltage your multimeter would have recorded would have been around 12.5 Volts that would have steadily decreased the longer the engine ran.
Now, if you're having to jump-start the pick-up to get it going, then you probably have a bad battery or a parasitic drain. A parasitic drain is tech-speak for something staying on (usually inside the car, for example: a dome-light) and draining the battery while the engine is off.
CASE 2: Your multimeter registered a voltage that steadily dropped down to 9 Volts. This is a clear indication that your Dodge pick-up's alternator IS NOT charging the battery.
Replacing the alternator at this point usually solves around 90% of the No Charge conditions on any Dodge pick-up around the world. That's right, you could stop testing here and say: ‘The alternator is fried’ and be done but..
I suggest two more easy tests to be absolutely sure it is bad. For the first test of the two, go to: TEST 2: Checking The Continuity Of The Bat (+) Cable.