Battery dashboard light - having trouble identifying the source

[5rivers]

The dashboard light for the battery is on and after charging it, light stays on! It is showing 12.4 volts, with car running, it’s showing 11.6 volts.
Cleaned all the connections (battery posts and clamps, and B+ connection on the alternator), marginal increase in voltage. Short of replacing the alternator with another j/y piece, i am wondering if replacing the voltage regulator might resolve the battery light on the dash.
Appreciate your input!

[PatternFlyer]

Your running voltage is too low. Most likely your alternator needs replacement. Yes If you can replae voltage regulator on the alternator, it should be fine.
Take the car over to auto parts store, they can test the charging system for you. I don't think there will be any charges.

https://www.matthewsvolvosite.com/repla ... n-the-car/

[Vova585]

First diagnose the source. Measure voltage properly. One lead at the body of the alternator and another at the center(as much as possible) of B+ terminal of the alternator. If your voltage is in 14.2V or similar- alternator is OK and you have to search where is voltage drop is. Positive of negative side. If your voltage is 12V with car running, remove the voltage regulator and inspect the brushes. Chance is that they are all worn. Then you have 2 choices. 1- Just replace the voltage regulator while alternator is still installed. 2- remove alternator and service it yourslef vs proper shop. Replace voltage regulator, bearings, serpentine belt. Do not give your old alternator as a core. Most of "rebuild" units are junk made in Mexico or china. So better service your old trusted unit.
Here is some wisdom from Eric O. It is slightly different system with ecu control, but he explains fundamentals well.

[erikv11]

In addition to proper voltage tests: Check the positive battery cable near the battery - is it hot after the car has been running? The cable at the positive battery post is another known weak spot in these cars, it corrodes internally, resistance goes up even more with the heat, mimics charging system problems.

[abscate]

Knowing how you run and where you run , in remote tundra of Northern NY….

Get the whole alternator off and bring it to a good auto electric shop for rebuild. You can buy the Bosch regulator from FCP. Then forget about it for another 150k miles

You don’t go far on battery power in these cars. An hour or two tops with a new fully charged battery , less at night and with an aged battery

[scot850]

FCPEuro only has a regulator made by Beru that has mixed reviews that supposedly fits 100 and 120A alternators. Issues including holes too small for locating screws and no connection for the dashboard warning light.

The do have 120A regulators from Bosch, but crazy priced OE one is on backorder with no ETA. Volvo seem to have regulators available at a very high price (what is new) but it says it does 100A or 120A but specifies 1999- only

https://www.volvocarstorontoparts.ca/p/ ... 67899.html

I seem to recall having difficult finding any that work for the 100A units as I have a rebuilt Bosch 100A unit that had a regulator made with brushes made of cheese and similar durability.

Repair shop may have a stash of Bosch or another brand they use as they will likely not fit a crap part due to warranty on repair (hopefully),

Neil.

[5rivers]

Thanks for all your replies!
I did install a non-OE voltage regulator but that seemed to emit a burning smell when I started and ran the car for a few minutes.
So, I took out that regulator and installed a used Bosch regulator that still had a decent amount of brush life. No more burning smell. But, the battery was sustaining only a trickle of a charge from the alternator, even after revving the engine up 2000 rpm for a few minutes.
With the alternator still on the engine and with the black cover removed, I decided to see if I could clean/brush the B+ post, the metal circular washer on the cover that the post goes through, and gave the alternator connection to the starter a good brushing, as well as the cable end from the starter to the battery, cleaned the battery post and cable connection, and since I had the cover off, I gave the diodes a light brush as well. I switched out the negative (blue) battery cable with another that was not frayed on either end, and doubled checked all the grounding straps for secure connections.
All that seemed to result in a better charging process as the battery voltage began to increase. It's now showing 12.8 and increasing to 13.2, 13.3, 13.4, etc. So, I am encouraged!!

[Vova585]

Glad to hear that are seeing improvement. However we are still not sure what is causing the issue. I would once again suggest ti revisit voltage drop testing on positive and negative side.(12.8v is ok, but you should be close to 14v. Plus was this voltage check with loads or wirhout?)You might find more issies that will gain you more voltage. If you will be sure about the source of the problem, you will be able to put your efforts into fixing it. And be confident that you did it and not just hope that you got it right. Good luck.

[5rivers]

Finally got the car back on the road after some PCV hose issue corrections!
I drove about a mile and parked the car. The red cable from the starter to the battery is hot. I checked for continuity before taking the car out and heard the solid sound from the multimeter, and resistance was low. But, the cable was surprisingly hot.

[abscate]

You can’t really check resistance on a high current wire with an ammeter unless you have an expensive setup.

With the engine running, look at the voltages at the back of the alternator, the starter, and the battery with lights on and lights off.

Draw a table of those measurements and see where the drops are and which lights are bad.