Hey guys, this is probably a simple diagnosis for you all, but I’m a newbie.
I drove my car 20 minutes so it was well warmed up. Stopped for gas, turned off engine, when I tried to start it up, it will turn over like a half turn. When I jumped the battery it started right up.
I changed the starter last year, the battery is two years old and shows 12 volts on a meter after I got home. The alternator is unknown how old it is. Does this sound like what happens when an alternator goes bad? Thanks for the help. —Billy

 

It sounds like your starter heat soaked and/or you have a bad ground or positive lead. If you have about 14V running, your alternator is fine

 

What are the symptoms when the alternator goes bad?

 

The most noticeable is the headlights dim and your voltage drops below 12V. When the battery voltages gets low enough it will no longer be enough to charge the coil and the engine will stall. If headlights aren't on, and the voltage is low enough, as soon as you turn the headlights on the engine will stall.

The easiest way to test it is to put a voltmeter across the battery terminals with the engine running and see what the voltage is (without the jump pack on). If you recently charged the battery you can actually watch the voltage drop if the alternator isn't putting anything out

 

At 12v, your battery is dead. I would start with giving the battery a good charge and cleaning the battery terminals and cable ends. With the engine running measure the voltage at the battery, should be around 14+/- volts. A fully charged battery is 12.6v, the .6 is very important.

 

My 87 musting with a bad alternator and fuel injection was still running at 8V...until I turned the lights on. But I totally agree, 14v is the number with the engine running

 

A battery reading 8v is not going to start an engine.

 

At 8 volts, your very close to the point where the computer will stop working. Simply hitting the brakes might be enough to drop system voltage to the point the ECM shuts down.

Clean the battery terminals, clean the battery posts. Put a trickle charger on the battery overnight. Reinstall the cables, put a meter on the battery terminals. Start the engine, with the engine running you should have a system voltage around 14.2ish. Turn on the headlights, heater fan on high, wipers, anything electrical. The voltage might drop a little, but still be around 13.5 or better. If not, the charging system needs some work.

 

^^x2^^ However you manage it (jump start?) get the engine running, measure the voltage at the battery. You should between 14.0V - 14.9V. If you are not, keep the car running, drive to the nearest automotive parts store, keep the engine running when you go inside. They will diagnose your alternator for free. Sounds like a bad alternator, IMO.

 

At 12.0V you have 50%.

 

I started the car today and with a slight hesitation it started. I metered the voltage on the battery before and it was 12 volts then 11 volts while running. Is that indicative of a bad battery?

 

Read above^^^. You must have between 14.0 to 14.9 volts when the engine is running. Your alternator is NOT charging your battery.

 

Opps I didn’t read that there were helpful responses above. Thanks for the help. I think the battery is bad if it’s at 12 volts then running at 11.

 

I would clean the terminals and let it run and see if the voltage continues to go down. It's still possible that he's got crappy connections and they aren't allowing the alternator to charge (I know it's not likely)


Not really. It's more likely that it's the alternator. A crap battery will still read 14V+ if the alternator is working

 

No. You cannot state that, as yet. If the alternator is not charging your battery between 14.0 - 14.9 volts, your alternator is bad. The battery will CONTINUE to run down if the alternator cannot charge the battery. Get your alternator checked - first.

 

Valid point. I was suspecting he had already (at least) cleaned the battery terminal ends. You should ensure you have solid (-) & solid (+) battery terminal wire ends on both ends of each battery terminal wire. I still suspect it's the alternator, but now would be an excellent time to clean your terminals. While you're at the automotive parts store, grab a battery terminal cleaner for $6 or $7 - they work excellent.

 

What may also be possible is the plug is disconnected from the side of the alternator. I had that happen to me more than one time over the years.

 

Check the condition of the cables, too, like tightness of bolts on terminals and corrosion.

 

Possibly, and in combination with a faulty charging system is a recipe for no charge/no start. Could be alternator, voltage regulator, cables, or battery.

Right now I'm leaning toward a bad alternator, with a bad battery cable or terminal next.

Noob Billy, do you know how to use a volt-ohm-amps meter? You can diagnose most electrical problems with it and save your car the indignity of a parts jockey who is questionably familiar with an older car's needs. We can show you the basics of using it.

Can't emphasize this enough. Get your own original printing hard copy of the 1968 Olds Chassis Service Manual. It has color wiring diagrams and covers about any service procedure you or anyone you hire to work on this car could need. You have to remember that most modern mechanics won't have a clue how to service a 50+ year old car.

 

After you have cleaned all the small and large connections at the starter, the battery, the VR and Alt whack the alternator with a dead blow or a piece of wood. Not too hard but just enough to unseat a possibly stuck brush. If it comes to life yank it and have it rebuilt by a local reputable starter-alternator shop. Check the alternator connections and ground on the VR.

I always recommend rebuilding components and staying away from the big box parts houses... especially if its original to the car or even close.

Also before replacing anything have the battery load tested after you manually charge it.
A static battery should sit at ~12.4-12.6VDC ish if its good. And it should take a load test without falling on its ***.

This tester not only load tests it also gives alternator output data: Good tool to have.

https://www.northerntool.com/shop/to...E&gclsrc=aw.ds

 

Can I test if an alternator is working properly by meter reading from the positive output to the block or negative?

 

He'd be able to tell that immediately if he could just find that OBD-II port and pull the codes.

 

Take your DMM (or DVM whatever you want to call it), put it the mode to read DC VOLTS. Connect your test leads to the meter, touch the other end of the black lead to the engine block or other chassis ground or NEG battery terminal, touch the red lead to either the battery POS terminal or the heavy red wire on the alternator (they both read the same voltage). With the engine OFF, a heathy battery will read MORE than 12V. With the engine running, a good alternator will read MORE than 14V, but it will definitely be higher than with the engine OFF. If the voltage does not increase when the engine is running, you have a weak or bad alternator. Its highly doubtful that a 2-y/o battery has gone bad unless you live where it is blazing hot all the time.

 

Unfortunately that ^^^ procedure does not test the functionality of the alternator it only tests whether voltage is being delivered to the battery. There are numerous YouTube videos available for testing an alternator. I have already suggested you take the car to an automotive parts store to make short order of having your alternator tested for free. Nothing could be simpler, IMO.

 

Old method that we used to quick test an alternator, with engine running pull battery terminal, if engine stops, problem is with the alternator or the connections to it. Working alternator will also create a magnetic field on the back side and can be tested with a screwdriver.

 

Har har har!!

my comment was directed to the comment about the 87 mustang.

 

Dont ever remove battery cables while the engine is running!! That’s a useless test, an ignition system only needs a couple amps of current to run. Obviously, a alternator that is capable of only a couple amps of output isn’t acceptable.

The screwdriver on the back of the alternator is a ok test if you have no tools.

A voltmeter is such a cheap piece of test equipment, there is really no excuse to not have one. A 10 dollar meter from harbor freight would tell you what you need to know.

 

There are only so many failure modes in an alternator. Either 1 or more diodes are bad (shorted or open), or brushes are shot. Failure symptoms of the various failure modes range from weak output to no output. You cannot deny that if the voltage across the battery does NOT increase when the engine is running (vs. engine OFF) points to the majority of the failure modes that are sufficient to result in a battery not receiving enough charging current when the engine is running. Certainly, obtaining a definitive test of the alternator at Auto Zone (or equivalent) is simple and easy, but the test I described is definitive: If the volts don't go up, the alternator is shot. Where else can that current come from to increase the voltage across the battery?

 

Your statements have already been recited a plethora of times prior to your post - read them (above).

 

Indeed, and yet the OP was still asking questions about how to test the alternator without going to Auto Zone. Excuse me for trying to help explain it in simpler terms, Chief.

 

No worries. We’ve explained it numerous times. My point was in relation to your statement, however. You can measure 14+ V at the battery and still have a bad alternator if the alternator is not delivering amps.

 

Thanks for all your helpful comments. I tried to have my local Autozone test my alternator and they refused, saying they were too understaffed to send some one outside the store to me.

The thing that I could not understand was why I could not read any voltage on the output + on a brand new alternator. No one has answered that question.
I had a friend who is a long time mechanic come over to look at it. He traced out all my wiring and traced the wire from the alternator that should go direct (or thru a junction block) to the positive on the battery. It didn’t go direct. It was routing thru a wheel well mounted solenoid. So voltage was not getting to the battery - it was terminated on the starter side. It’s been corrected and is now working perfectly. The battery is showing the proper 12.6 volts off and 14 ish running.

How did the incorrect wiring happen? Last November before putting the car away for the winter, I got stuck with a shorted out solenoid at a car show. In haste I acquired another and had a few car show people help me change it. They must have put the wire on the wrong side of the solenoid. So I guess I’ve been running off the battery for the few times I took the car out over winter and now into the spring.

So though my problem is not the alternator, I still wanted to know why I wasn’t reading voltage out of the alternator even when it wasn’t connected back to the battery. The way I’m understanding it now in simple terms is that the alternator won’t out put voltage if the internal regulator detects no load or an open circuit. As soon as I connected the alternator to the battery directly, it showed voltage at the alternator terminal. —Billy

 

Remove cables for troubleshooting for forty years, do not not knock someones comments if you do not have a clue about what your talking about.

 

Ok smart ***. How many different links do I need to share before it sinks in?? This isn’t an Edsel the OP is working on.

https://www.familyhandyman.com/proje...an-alternator/


https://mechanics.stackexchange.com/...car-is-running

http://www.madelectrical.com/electrical-tech.shtml


https://ricksfreeautorepairadvice.com/testing-alternator-by-removing-battery-cable/


If this isn’t enough to convince you your testing methods are out of date, less than conclusive, dangerous and potentially expensive to repair, do a little research on your own and broaden your horizons.

if you have been turning wrenches for forty years, then you should have learned long ago that NOBODY knows everything. Only an arrogant *** would assume they know everything, and are unwilling to accept that maybe someone knows just a little more about whatever the subject might be.


I guess my 35 years of turning wrenches pales in comparison to your 40. I hang my head in shame.

 

Glad you got this problem resolved. Hate it was so convoluted and that an emergency repair went screwy. But, no education is wasted!

 

The alternator should be connected to the horn relay junction power strip with a spliced wire to the voltage regulator. There should also be a wire that runs to the battery and the bulkhead connector that has a fusible link on the end. What sounds like happened is the connection at the horn relay terminals was corroded and not allowing the alternator to charge the battery.

 

Have a nice day!

 

Glad you figured it out, it is usually something simple with this old cars. Wiring is probably the toughest challenge we face on cars.

 

Matt, I agree with the principle, but in reading the second link you posted the danger is potential damage to the vehicle's onboard electronics. While the OP doesn't have an Edsel, his 1968 442 certainly doesn't have all those electronics mentioned in the article. I'm not meaning to start a fight, just pointing out there aren't very many (any?) electronic systems that could be damaged in a '68.

 

87 is long before OBD2...