Charging System Basics
Before driving down to the auto parts store and buying an alternator, then going back for a battery, only to find out it was the voltage regulator that failed and cooked everything in the first place, it is best to test the charging system first! This three part system is the key to electricity in the modern automobile. If any one of these three parts fails, then the charging system fails.
- Battery: Stores electricity to turn the starter and kick over the engine when the ignition key is turned. Batteries will fail over time, or due to lack of maintenance.
- Alternator: The belt-driven alternator produces electricity once the engine is running. This exposed moving part is prone to failure.
- Voltage Regulator: Balances and controls the flow of electricity from the alternator, and is often integrated into the alternator itself on modern automobiles.
Bad Alternator?
The alternator makes electricity for the headlights, ignition system, engine control computer, and the very large array of computers and phones plugged in the cigarette lighter. The alternator sends any extra electricity to the battery for storage by way of the voltage regulator. The then battery returns electricity to help out during times of heavy demand. If the alternator stops making the juice, excess demand can drain the battery and leave you without a car that starts. Checking out the charging system can be done with a multimeter, charging system tester, or similar method. The service manual is your friend. You can also drive down to the auto parts store and have them check out the charging system. Bad alternator? Follow along with the step-by-step photos for more tips on removing and replacing an alternator.
Tools and Equipment
- Service manual
- A multimeter or fancy charging system tester.
- Some wrenches and hand tools
- Safety glasses
- Ramps or jack and jack stands if the alternator is under car.
- Battery load tester or similar
Step-by-Step Tips for Removing and Replacing an Alternator
Since it’s not mentioned in the article a quick way to test with the multimeter is as follows. With the car off check the voltage across the battery. Should be 12+ volts. Anything in the 10 volt range points to a discharged battery. If battery discharged charge with battery charger or jump start car. Once car is running check the voltage across the battery again. At this point you should see 14 volts across the terminals. If you see 14 volts then it’s a pretty good sign that the alternator is working but your battery may be bad. If you see less than 14 volts then the alternator probably isn’t working and your battery is most likely okay just not being charged by the bad alternator. As to the voltage regulator I have no experience with them as seperate items as all the cars I’ve ever owned have had them integrated into the alternator.
Thanks Tanj. Another test is to run the multimeter positive from the alternator, then negative to battery/body ground. That being said – every car is different. Especially 6V systems, Positive Earth, and so on. A test that works fine on a 1967 Dodge Dart can wreck havoc with modern electronics. A shop or service manual will outline specific voltage and charging system testing procedures. For the junk we drive these books can usually be found for under a sawbuck. Shameless related and promotional link below.
Find a Shop Manual
Alternators are wear items. They are not designed to last forever. If automakers designed alternators to be serviceable or last a lifetime, they would be orders of magnitude more expensive. Alternators are cheap. There comes a point in time where the brushes will wear out, possibly the slip ring too. You can find replacement parts for some alternators online, but they still weren’t designed to be serviceable. It is difficult to pull apart an alternator without breaking something. In the least, you have to re-solder components to make a repair and put it back together. It is way easier to just buy a new one and send the old one off to be refurbished.
What is it about Dodge electrical systems, ya know? My old Eagle Talon was essentially a Dodge Neon under the hood. Where’d they park the alternator? Under the intake manifold on the backside of the engine. I’m telling you guys, you needed stereo instructions to navigate the old one over, under, around, and out through the wheel well, and then a healthy spoonful of swear words to get the new one in. Oy.
Just did some electrical testing on the in-laws GM failbucket a couple weekends back. I generally keep a couple rules of thumb in mind…
1. If I can jump it – and it stays running – probably the battery.
2. If I can jump it – and it won’t stay running – probably the alternator.
3. If I can’t jump it – and we can’t push start it (stick shifts only) – probably the starter.
Beyond that, I’d add that it could be useful to disconnect the positive side of the battery and check for current while the engine is off. If you’re pulling amps across the gap between the positive terminal and positive battery post, it’s a good sign that you’ve got a short somewhere slowly, parasitically draining that battery.
Electrical gremlins are the worst.
Parasitic drains are most likely the diodes in the alternator itself…or the underhood light…or the dome light.
Wonderful thing about old Chevys is I can buy the kit at discount auto with the important innards in it for a fraction of the cost of a rebuilt.
Something else to check for on many older cars- the “ALT” or “CHARGE” lamp. Easy enough to check- switch on your ignition, and look for the light. If it doesn’t come on and you are experiencing charge problems, check that first. Many systems switch the alternator on through that lamp. No lamp = no work.
You also get what you pay for. I went through 6 (six!) Pep Boy’s lifetime alternators. The alternator light came on for Alternator #4 a month after I bought it. I grabbed the breaker bar and the two wrenches I needed and changed it in the Pep Boys parking lot, on a 95 degree day, in my work clothes.
Alternator #5 lasted two blocks. I returned and gave the manager an earful. He swore up and down that they had a 2% return rate and that I must have a MASSIVE electrical problem.
I asked if he had another on the shelf. He did. I told him to put it in the tester. It failed.
I told him “I must have one huge [deleted] electrical problem to take out an alternator FROM THE PARKING LOT!”
The AC Delco that replaced it was also a Re-man, but it lasted a good 7 years, and honestly, I don’t blame it for it’s ultimate failure. The last time I rebuilt it myself…that was a pretty neat experience and Youtube has several videos on what steps are involved.