My battery/alternator light just started coming on at idle, and goes almost out when at driving RMP's. If I turn on the blower fan it stays on consistantly. I originally thought that the alternator was on it's way out. But with the headlights on, I just noticed I can't change from low to high beams, it stays on high beam. It will flash high beam with the lights off, but when I turn on the lights it is stuck on high beams. I can hear the relay when I pull the high/low beam lever, but nothing happens to the lights, stuck on high beam. The alternator is only about 6 years old at 5K per year of driving. Any suggestions? 1982 245

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crikman

If you have a voltmeter, please take a couple measurements for us.
With the engine idling, measure across the battery terminals. It should be 13.5-14 volts.

Also, from the alternator's output terminal to it's case.

Then, with the engine off take a resistance measurement between the alternator's case and the engine block.

If you don't have a meter, an inexpensive one will do.

I cleaned all the ground connections, polished them to a shine, and coated with dielectric grease. No more alt dash light, even with blower on high and lights on. Oh, and the high/low beam switch is performing as it should. I took some of the readings as recommended - Voltage between battery terminals with engine running 13.04v....Could an old battery cause the voltage to be under 13.5volts? Engine off alternator housing to block- 0 ohm resistance. I haven't done the engine running- alternator output to to its case yet. I'll try it tomorrow. Is that the bigger wire off the back side? Just to note, voltage between battery terminals with engine off was 12.05 volts. It is several years old and as machineman mentioned, it may have been compromised a bit.
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crikman

Hi,

It sounds like you got the "gremlin" on the run!
I'm glad we helped you out!
Thanks for the thread too!

Another way to check for bad connections is to use your voltmeter on BOTH sides or terminals of the battery to various ground points on the car.
On the negative there are two. The body and the engine block.
When the leads of the tester are on the SAME SIDE of polarity, the meter should read 00.0 in a "perfect" circuit, that probably doesn't exist.
In my world of machining, we can only try to do that!

What you should see is 00.02 and a few hundreds more only.
By the 00.2 reading, that is way too much on any ground circuit, in reality.
What this is telling you that in affect you have a resistance that an Ohmmeter cannot show you unless you are directly across it with its own battery circuit.

This technique checks the overall health of the circuit in use.
Like the big battery cables that are connected and power being used on their perspective ends.
When the circuits are actively live and flowing current this will show its amount of resistance by not being totally zero.
This tiny number change means "exponentially" there is higher resistance as it goes up. Much like the numbers with the Corona Virus, it means big trouble is there!
The slight error, from all Zero's, is caused by the meters own internal workings and wire resistances.

When you checked the alternator's housing to the negative terminal of the battery expect a ver low reading and it means you have a good ground.

The voltage on that battery check you made, 12.05V is saying to me, that it's not charging up up very well or not holding its charge very well.
That is a LOW battery charge condition reading, unless you left something on for a while before doing that test ACROSS the battery terminals.
A rested battery is fully charged @ 12.65. Right right after a shut down it should stay up higher like your reading of about 13.2 to 14.2 for a while and then lose the higher "residual charging voltage" readings over time or until you have something on for a short period of time, it goes away quicker.
You have a normal "operating" voltage it seems.

I suggest you keep an eye on that battery charging system, to see if "rested time voltage" improves or you might just go "click only," in the near future!
Anytime the voltage is "always" hovering @ or below 12.42, I worried about the age of a battery's capacity!

This is especially so since, I try to keep a battery maintenance charger on mine, if I don't drive it regularly. I have gotten 11 to 14 years out of almost every battery I own nowadays, since I learned this much more over the years.
A good grade of electronic maintainers make it simpler and a good investment.
That is, if you don't get caught up in some hyper salesmanship and buy from the wrong sellers!
It's like some hearing aids companies, "they CHARGE what ever they can get!"

I shop around and have settled in on Battery Tenders line of products bought from Costco.
Costco sells for less on lots of things but I have notice that newer models come out shortly there after. Now they hype all the types of batteries it can charge automatically! Marketing!

Today's consumer have to play the ends against the middle "on close outs."
Needless to say, I drive the 240s, For what ever I can get too! (:)

Phil

Obviously you have corrected the poor connection. The exact charging voltage across the battery will vary slightly with temperature to protect the battery from over heating in hot weather. If you are curious there are graphs of charging voltage vs temperature in the Volvo Green Manuals. I would say if your battery is maintaining 12V overnight then both the alternator and battery are fine.

Just asking, does your alternator have the old external voltage regulator that's mounted on the right fender or the integrated regulator and brush unit mounted on the back of the alternator?

There are so many connections in the total wiring harness that there are seemingly endless little voltage drops around the car. The fuse panel is a mass of connections. Some day you might consider cleaning and coating those. It's also important to check that area for corrosion from a windshield leak.

I drove the car about 45 miles today and rechecked the voltage across the battery terminals- 13.4v with engine running, and 12.7v with engine off. The other day when I checked it I had only driven about 7 miles after the cleaning. So it's going the right direction. Thanks again for all the info, much appreciated.
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crikman

Thanks for the info. My alternator has the internal regulator/brush assembly mounted on the back. I used DeoxIT spray on the fuses giving them a spin in place. I used DeoxIT on a few other push on connectors I found in various places in the engine compartment, spraying then unplugging and replugging them a few times. I use that stuff all the time doing guitar repair. I can't tell you how many times it has saved the scratchy pots in a vintage Gibson or Fender. Replacement seriously affects vintage value. Anyway, I ran out of dielectric grease after coating the major connections, but I'll take your advice when I get some more and use it on the fuse connections. Thanks all for great advice that was spot on. One of the most satisfying fixes I've done in a while, and it was basically free. Gotta love the Brickboard. You guys are awesome.
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crikman

Hi,

Do the most obvious first with the alternator check for the belt not being tight.
I try to spin the alternator's fan and pulley setup under the belt by hand and get it tight enough to just be able for it not to spin. This makes it easier on the bearings.
You said the alternator was 6 years old and low mileage so the brushes should still be good unless it was poorly rebuilt.
The idiot light can come on weakly due to a belt or a poor ground wire from the alternator housing to the engine blocks contact point beneath the housing.
The idiot light is just what it is as it works when it already a problem.
This may have been going on for a while.
The regulator needs to see the load voltage of the whole system in order to adjust it correctly.
So that means down there and on the output to the battery. Make sure all cables are clean and tight everywhere at the ends of those big cables.


The headlights may have an issue with the relay on the drivers fender.
It's a mechanical toggling arm or bar that might be stuck inside the relay.
It can thunk when the magnetic power pulls it but it stops moving anyways.
Old relays can get sticky in there from wear and moisture. It happens from a great deal of non use or the connector and terminals are corroded underneath.
Open it up and play with it and you will see what I mean.

I hope this helps as it seems it need a little TLC and a Voltmeter installed on the dash gives you a continuous update to the charging systems health.
Batteries suffer a shorter life if not kept topped off regularly.
The late seventies and early eighties cars had a smallish charging system capacity, IMO, so it requires a watchful eye on driving the car a lot and regularly and it's Ok.
Today's battery maintainer and chargers are a good backup for low usages or plain battery up keep.
Done religiously you can double the life of a battery.


Phil

That's great advice on the ground straps. I can hear and feel the headlight relay actuating, but maybe with insufficient voltage the it isn't working to it's full extent. I'll check those grounds tomorrow Thanks much..
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crikman