No Battery Light, Alternator should be good

[Croley]

Well, I was getting around 12 with the car off, 12 with the car on and 11.7 with the lights on, so i'm guessing regulator? which i dont know a thing about...

[epmedia]

What does the voltage read at about 1100-1200 rpms with the lights off and on?
The regulator is attached to the back of the alt with 2 screws.
It's the ting with the brushes on it (inside the alt).

[Tom D]

or could be the brushes are worn out. there is a section in the hays manual on replacement.

[Croley]

I had the brushes replaced... so ill check the voltage at 1100 rpms, i think my idle is normally there and some times higher, which i still havent been able to find the screw for it, and i still dont have a haynes... they are hard to find for an e21, i guess i just gotta get it online

[epmedia]

According to the Haynes, the alt starts to charge at about 1060 rpms for the stock '80-83 model alts, in which the voltage should show way above the "engine off battery voltage", with the headlights on (as Tom described earlier). Double check that ground wire to the alt too (before replacing parts)! It probably is the regulator, but do the checks, first.

[bimmer1985]

I believe I am having exact same problem with my 85 and still can't find a solution. My battery kept on dying replaced belt. Checked voltage was not so bad. Took it to Advance to get a full checkup was told alternator needed replacing. Got the alternator reman. Installed it only to find the voltage at the battery is unaffected by the presence of alternator. Battery eventually dies. Checked continuity on the thicker cable going to alternator to + batt terminal and checked out good. Checked voltage accross the thicker wire and ground same as batt. Checked voltage between thinner blue wire going to alt and read same as battery voltage. Therefore the alt does not seem to be doing anything?

By the way, the battery bulb is working properly. It barely lights up as I turn ignition off. What could the problem be? Any ideas?

[Tom D]

grounding problem

[bimmer1985]

The casing should be grounded so I checked the continuity between the casing and the car chassis and everything checked out. Could it still be a grounding problem? Where would I start looking?

[Croley]

well 1985, i think we are in the same boat... :/ I replaced the regulator... same deal... 12.40v off and around the same on... im going to check on the excite wire and make sure there is a connection, also i checked the grnd on both the alt and the grnd wire it is going to and it is solid... apart from the excite wire im clueless

[bflan2001]

seems like charging issues are more of a problem recently...i just replaced my entire charging system and finally found it was a bad excite wire...so i replaced that and it charged great, for a day..now i'm back to square one with a completely new charging system (battery, alt, grounds, wiring) and no charging voltage

[bimmer1985]

Checked the resistance between alternator housing and negative terminal as well as alternator housing and chassis and both gave me .1 Ohms. I the proceeded to run the car and undo fuse by fuse to see if perhaps I had a short in any of the circuits. I had the voltmeter connected to the battery while I did this hoping to see a voltage spike but nothing. I suspect a bad wire somwhere.

After a week messing with it I decided to give up. Off it went in a tow truck to the shop where it will get fixed. I will let you know as soon as I find out what the problem is. Hopefully it will help you out as well. I know how frustrating it can be.

[epmedia]

Sometimes the excite wire breaks at the terminal, under the insulation (especially if the alt vibrates from bad bushings). You folks be sure to check the charge wire connection at the starter motor, and the light bulb on the dash too. Everything else has been covered

[Croley]

yeah, today I figured I'd do some diagnostics... I got no where... the excite wires should be good, there is power going through them and the end terminal should be good. the ground is still good, and the connection to the battery is live... Possibly the relay is shot? idk, ill have a look see... nope same deal, but i think i might be getting somewhere, because i dont remember hearing my car click when turning the ignition... and the pondering continues...

[bflan2001]

i ended up parking my e21 last week for the first time in a looong time because of this stupid charging problem...i'm back in my other car, dying because i know the e21 would love to slide around these summer rain-soaked roads

i'm very interested to see what you find, and if i somehow find the motivation to dig back into mine, i'll post any findings in this thread

[Croley]

Monumental Breakthrough... Not a solution yet... but i feel like an ishmo now... while the car was running i checked the back of the alt and got 14v!!! and then went to the batt and still got the lousy 12v... im still confused why that is... but the alt works and puts out charge, now i am wondering what is causing it to not charge the batt... wiring? idk cause the engine is running off the batt not the alt, i can tell when i turn on lights and definately when the battery is low i can feel lack of power... errr... any ideas???

I hooked the alt grnd up to the batt grnd and that didnt change anything, so i hooked the red pwr wire up to the battery and then the batt got 13v so maybe im getting somewhere

should i just hook a batery wire from the back of the alt and hook it up to the batt? or is that not a good idea

[Tom D]

too much resistance in the battery cables.

where is the battery located?

did you ground the battery to the rear shock mount bolt? if so drill a new hole in the body and re-ground it.

check the resistance in the positive battery cable.

clean the positive lug/wire at the starter.

[Croley]

the battery is in the front left right by the engine and air intake/oilfilter/alt

http://i79.photobucket.com/albums/j1...5312011537.jpg

I'm not sure about the resistance and ill check the starter wire... its so weird cause it seems like there is a +wire touching a grnd place somewhere therefore the red+ that gors into the back of the alt even tho it is being fed 14v is not putting it thru to the engine and batt... and it was all fine before i decided to be an electrician and re-wire the naked wires, i shoulda just put some electrical tape on it and call it fixed... cause now 2 months of charging my batt and $80 later nothing is different haha

i think its the isolating piece, the guy who replaced the bushings and whatnot didnt put it back on... :/ 12311356217 should be the part#

VICTORY!!! the culprit was the l;ack of the isolating piece... so i got a piece of plywood (im not at home and dont really have toold) took a nail and hammer and made a hole to screw the wood onto the bolt... then it still didnt work, so i took apart the wire going to the back of the alt and found this mess https://fbcdn-sphotos-a.akamaihd.net..._1703953_n.jpg it got fried, so i replaced it and botta boom botta bing https://fbcdn-sphotos-a.akamaihd.net..._4570076_n.jpg It's getting at least 13v to the batt!!! who hoo... i hope this is the end!

[Tom D]

yup, too much resistance. now replace the cable. you need to see between 13.8 and 14.8 volts.

[bimmer1985]

the battery is in the front left right by the engine and air intake/oilfilter/alt

http://i79.photobucket.com/albums/j1...5312011537.jpg

I'm not sure about the resistance and ill check the starter wire... its so weird cause it seems like there is a +wire touching a grnd place somewhere therefore the red+ that gors into the back of the alt even tho it is being fed 14v is not putting it thru to the engine and batt... and it was all fine before i decided to be an electrician and re-wire the naked wires, i shoulda just put some electrical tape on it and call it fixed... cause now 2 months of charging my batt and $80 later nothing is different haha

i think its the isolating piece, the guy who replaced the bushings and whatnot didnt put it back on... :/ 12311356217 should be the part#

VICTORY!!! the culprit was the l;ack of the isolating piece... so i got a piece of plywood (im not at home and dont really have toold) took a nail and hammer and made a hole to screw the wood onto the bolt... then it still didnt work, so i took apart the wire going to the back of the alt and found this mess https://fbcdn-sphotos-a.akamaihd.net..._1703953_n.jpg it got fried, so i replaced it and botta boom botta bing https://fbcdn-sphotos-a.akamaihd.net..._4570076_n.jpg It's getting at least 13v to the batt!!! who hoo... i hope this is the end!

Not to jinx it or anything but whenever I was working on mine I was getting close to 13v out of the alt. However to the battery it was still 12.86. Yes there was resistance but I don't know why voltage was still low it should have been higher. I'd say take it for a spin and see how it behaves. Make sure that voltage doesn't drop again.


I called the shop and they told me it was the alternator. However, I am not convinced. The alternator was reman by a friend of mine who tested the alt for 45mins. There's the possibility something might be wrong in there or there's a problem elsewhere. In the meantime they will try a different alternator. I will have to take a look myself and see if the voltage is above the 13.5 the alt should be putting out. I will check resistance between the wires again. I hate electrical problems

[epmedia]

yup, too much resistance. now replace the cable. you need to see between 13.8 and 14.8 volts.

Tom has the ESP, yes?

[bimmer1985]

I went ahead and replaced the aux fan this weekend. It still not behaving as it should but I was able to get it running in the low setting. Even at high the voltage does not get below 13v and at 2000+ revs it is usually around 13.5v. Who would have thought this was causing me all these headaches. Even with everything ON, radio, AC, and lights at idle the car doesn't die anymore.

[Croley]

Ugghh, so when i fixed the car i was at the nc coast and i drove 4 hrs on 1 battery, idk how it made it, but yeah i fixed it and that night the one time i forgot to lock the door, someone stole my multi-tester, battery charger and ipod... some people... im glad they didnt see my flatscreen computer monitor that was in the back seat... sad day after the victory, but i havent had a chance to check it again... i will tho... but thanks for all of your input and esp

[DPDISXR4Ti]

Hope you don't mind me crashing this old thread. I'm dealing with a 1988 Merkur Scorpio which uses pretty much the same Bosch alternator found in Bimmers of the same era. Everything was working reasonably fine, but I'm switching to an electric fan and that required an alternator upgrade. Others have used a more modern Mitsubishi alternator spec'd for a Nissan as a good replacement, and so I have been going down that same path.

The new alternator is installed and seems to work fine - I'm seeing 13.8 volts on my cigarette lighter gauge - but my battery light on the instrument cluster is staying dimly lit. Alternator diode was bench-tested good at around 600 microvolts. Any thoughts on a diagnostic path?

[320iAman]

I'd check the D plus wire at the alternator, alternator rectifier needs 12V constantly, its also called exciter wire, you say 13.8V at cigarette lighter, check the alternator at the battery posts should be 14.2-8V after the start up and then come down to 13.8V after the battery is recharged from use by the starter which typically uses around 200Amps from the battery to start up.

The alternator light is shut off by the diode trio sending 12V up the D plus line when the alternator is spinning, that way the light is shut off as there is no grounding. When the key is on before start up the alternator light is illuminated as it grounds to the alternator case.


Randy

[DPDISXR4Ti]

Thanks for the input Randy. I've checked the integrity of the D+ wire end-to-end, right up to the bulb contact point at the back of the instrument cluster and it's showing .7 Ohms. Mind you, that was going through a couple alligator-clipped connections on my test leads. I don't think that's the problem.

I suspect I'm getting a bit of a voltage drop to my cheap cigarette lighter gauge, so I imagine I've got 14.x at the battery, but I will verify. Either way, it does show that the alternator is working and charging the battery.

I do get a full bright illumination of the battery light with key on (before start-up), and then it goes to dimly lit once running.