Alternator not charging

#1

On my 87 325i beater: Battery wouldn’t charge so i Had installed a new alternator 2 weeks ago and charged battery fine got 13.5V at idle at the battery… ran great for awhile. 3 days ago car died - below 12V at battery while idling.

I cleaned up various ground terminals, both battery terminals and the fuse block near front right of engine bay. No change. Even ran a new ground strap directly from the alt. to the nearby ground on the left of the engine bay. Touched voltmeter directly to large post on alternator (running at idle) and other to ground - same voltage as at the battery - eventually as low as 8.5V yet still running. Convinced myself alternator was suddenly no good and AutoZone gave me a new one - still the same.

It’s like the alternator is not even connected. Tested the same large post on alt. on track E30 and easily got 13.5V while idling. I am stumped. I read all about the exciter “battery light” in dash so i checked that - turns out there never was a bulb in there (but car did charge without this bulb previously). Also read that after 87 this bulb doesn’t matter.

This has got to be a simple wiring issue but i am ready to take it to a shop cause i can’t find it.

Any ideas?

#2

Check exciter voltage at little screw behind alternator. Does it have 12V at Key-On? While running?

If exciter voltage seems to check out, check the V regulator. It’s in the back of the alternator held in by two screws. It has two big “brushes” on it that wear out. If they seem worn way down, buy another V regulator. Usually the symptom with worn brushes is “intermittant” problems tho, not cold stone dead.

If neither of the above get you anywhere, do some reading at e30tech. If still no answer, get a used alternator from someone in your area. I could put one in a USPS flat rate box for you, but you probably have resources closer than me. Better yet, buy one from Al Taylor. He’s probably got a dozen of them and he could use the money.

#3

I somehow fixed it. I replaced the non existent bulb on the cluster behind the battery symbol, figuring maybe the resistor burnt out and I couldn’t find that so the bulb would take it’s place. fired it up and the battery light never went on, but now it is charging at 13.5V idle.

Where exactly is the little screw behind the alternator to check exiter voltage?

Also - what are the two long fuse-things (red and green?) in the ancillary fuse box thing - that little 2" square box with the knurled nut on top? They looked pretty corroded - i turned them but didn’t clean them.

#4

[quote=“RacerDan” post=70120]I somehow fixed it. I replaced the non existent bulb on the cluster behind the battery symbol, figuring maybe the resistor burnt out and I couldn’t find that so the bulb would take it’s place. fired it up and the battery light never went on, but now it is charging at 13.5V idle.

Where exactly is the little screw behind the alternator to check exiter voltage?

Also - what are the two long fuse-things (red and green?) in the ancillary fuse box thing - that little 2" square box with the knurled nut on top? They looked pretty corroded - i turned them but didn’t clean them.[/quote]

As you know there’s 2 threaded studs coming out of the alternator. One takes a 13mm nut and one is small, maybe 8mm maybe 10. The small one is the exciter.

The aux fuses are for optional equipment. You can delete that little box unless you’re using it to run your subwoofer.

#5

The small one is the “D+” Terminal i figured out while researching. How do you test that? Put key to position 2 and see if there is voltage?

#6

Yep, there should be close to battery at D+

FYI: the cut in date for the cluster with the resistor bypass is well after 87.