I have a 1984 Volvo 240GL with automatic transmission. The last two days I have been seeing my alternator no-charge light (red battery light) come on intermittently while driving with the headlights on. I drove with headlights off this morning and the light did not come on. The battery was replaced last year. I have had the car 4 years and never replaced the alternator.

I checked the following and all are fine:
battery cables, alternator wires (at alternator), alternator pivot bolt, fuses, and drive belts.

I also checked the charging system with a voltmeter:
Car off, battery: 12.3V
Car on, no lights: 13.8V
Car on, lights on: 13.6V (does not go back up)
Car on, High Beams: 13.5 (does not go back up)

My question: Can an intermittent no-charge light be caused by an alternator that is starting to go bad? Or does this usually happen all at once?

Please recommend the best way to troubleshoot from here.
Thanks,
Kyle

 

I assume those were measured at the battery ... so now measure both posts on the back of the alternator, using the fender for a ground, while running (idle). Then measure the case of the alternator, using the fender for a ground during idle.

It could be one of several things .. these measurements will narrow it down.

 

Sounds like the alt brushes might be getting low. Or the regulator is about to go. Happened to me on another car. Intermittent voltage fluctuation and I just kept driving. About a week later the car died at a red light left turn lane. Not fun. Replaced the alt and fixed it.

 

Thanks guys. I will check the things you suggested and reply.

 

OK, here is the results from bubba240's suggestion:
Posts on back of alternator with car at idle-
Large wire: 13.91V
Small wire: 13.96V
Case of alternator: -.135V

I did pick up a new alternator that can be returned if I don't install it...the paper inside suggested checking the wires with the car off.
It says Large wire (B+) should be battery voltage: reads 12V (OK)
Small wire (D+) should be AT LEAST 2 volts with ignition on (engine off): reads 1.65V
The guide says "lower voltage readings will prevent the alternator from charging...check D+ wire for breaks" I do recall fixing this wire in the past...insulation was falling off, so I used some heat-on insulation and put a new connector on.

With these readings, is the D+ wire more likely my problem?

 

Let's back up a little. Does the car pass the dash-light test? With the key in KPII, key position II, not cranking, engine off, you should have a Christmas tree on the dash lights: Batt, Oil, Parking Brake, Brake Failure, and Bulb Out. Do you have those five lights on?

 

Yes all lights are on including the battery light with the ignition on (not cranking, engine OFF). As I was making the tests last night, I cleaned the lead on the D+ connector and added a small amnt of dielectric. I also checked and wiggled all the fuses. This morning I made my 40 min commute with headlights, fan and radio ON. My bat light never came on.

Do the readings I took from Bubba240's reply look OK?

 

So those readings are almost exactly what I measure on my car. I replaced the regulator and brush assembly about a year ago.

Most likely one of your connections is (was) loose. Hence you wiggled the wires and the light didn't come back on. The one to watch is the blue wire ground that runs from the bottom of the alt to the block.

Since you have 13.8V at idle ... I would say your battery is charging and you don't need another alternator. But the brushes will someday wear out ....
http://www.fcpgroton.com/product-exe...ategory_id/112

I should note that when my brushes were worn, and only slightly charging ... never did any of the lights come on. Thats because that light is hooked to the battery on one end, and the alt on the other. I will only show you the difference between the two voltages ... current flow through the light.

Then while driving the gas guage suddenly dropped to nothing which freaked me out. Then the radio got real quiet. Then sputter, sputter, stop.

 

Thanks for everything. I will return the alternator and continue to watch the circuit. I did have the ground wire break off before which left the car dead on the interstate (not fun). One more question on the subject:

Is there any way to know how long the brushes on the voltage reg will last? Or is there a way to test how worn the brushes are?

 

From Bentley: "Brushes shorter than 5mm (0.2 in.) should be replaced" and it shows someone measuring how far the brushes are sticking out of the assembly with a ruler.

One of these days I'm going to install a volt guage for stuff like this.

 

Something that hasn't been mentioned but that is very likely is an intermittent short between the battery and the alternator. For some reason, the wiring harness is routed right underneath the engine and regularly melts together. The symptoms of the short are the battery light coming on while running or other funny dash board light behavior.

Also NOTE: if you test the alternator while all the cables hooked up, you'll get confusing readings because of the short in the harness. If you go to Pepboys or some place for a free alternator check, make sure you disconnect everything first, otherwise they'll just tell you that a new ($300) alternator will solve everything.

I've pulled this mess of shorted wires out my car and it wasn't pretty.

 

On my 82 245 wagon, just the parking brake light comes on with the key in the II position, and the alternator doesn't charge at all after a I replaced it. Have not checked the harness running under the engine. Is there away to check it without looking under the engine?

 

this was a 4 year old thread....

you pretty much need a volt meter to check a charging system.

fully charge the battery with whatever your charger is, and disconnect it, and let it sit a few hours. use the meter to measure the voltage across the battery terminals, it should be something like 12.6V.

turn off all accessories (headlights, stereo, etc), and start the car, and measure the battery voltage, if the alternator is working, it should be about 1.3-1.5V higher, like 13.9V. if it is, everything is working correctly.

the alternator light should light up when you turn on the key, and it shoudl go out once the engine is running. if the light doesn't light up, the D+ circuit is bad. this could be the dashboard ligthbulb, the ignition switch, the wiring, or the diodes inside the alternator. if the light does light up but doesn't go out when the engine is running, this means the alternator isn't outputting any juice, which could be the diodes, brushes, regulator. it also could be the alternator ground.

if your new alternator isn't charging, check the D+ circuit to the Alternator light on the dashboard. When you turn the ignition key on, the D+ terminal on the back of the alternator should be + volts relative to engine ground.

When the engine is running, put a volt meter between the battery (-) terminal at the alternator metal body. if there's more than a fraction of a volt between these, check the ground wires at the battery and the alternator.

 

My alternator is good. With my key in the KPII key position, none of my panel lights work except the parking brake. Is my ignition switch bad? 245DL wagon, 1982. My ground from the alternator to engine seems fine.

 

I suppose it could be the switch then... but kinda weird as the parking brake light is powered from the same wire on the ignition switch as all the other lights.

sadly, I don't have a 1982 wiring diagram, only 75-80 and 84+

the 1980 diagram is a lot simpler than the 1984, but on both cases, the instrument panel lights are ALL powered off the ignition switch via fuse 13, the switch in turn gets its power off a heavy red wire that comes from the positive terminal under the dash on the left fender, on the relay strip.

 

Thanks, I will chase the wires you speak of down and check them and pull the dash off to check the bulb. Does the battery bulb really interrupt the circuit?. The next step will be to figure out if it's the ignition switch and figure out how to pull it out.

 

the alternator light is wired to the ignition key on one side, and the alternator's D+ on the other side, when the key is on, current flows through this and lights the bulb... when the alternator is turning, this current serves to jumpstart the field winding, once the alternator is generating its own power, the current goes to zero as the alternator's output voltage is now the same as the battery voltage, and the light goes out.

 

I had the INTERMITTENT battery light problem in my 1984 "245." I replaced the alternator with a used one and had the same problem. I noticed the fuel and temperature gages were not working. I figured there must be a bad fuse so I found which fuse the exciter wire for the alternator went through. It was fuse 13. When the car was working fine without the problem I disconnected fuse 13 and the battery light went on and the two gages stopped working again! I cleaned the corrosion away from the fuse holder and put a new fuse in. I think the battery light can go on when the exciter fuse is corroded.