Long-time- no-post!
Hi all.
Just took the car out of storage from winter, looking forward to driving.
My new battery keeps draining overnight.
So I tapped in-line my multimeter and started pulling fuses and relays to locate the source.
When I pulled the alternator wiring harness plug from the relay board, the volts/amps dropped to zero. Bingo!
But now what do I do? Do I have a bad alternator or can I diagnose further?
Thanks for the help.
I'd hate to have to struggle to replace that bad boy for nothing.
Steve

how far are you from Tyngsboro?

diode in the alt is blown and is energizing the field from the battery. get a new alt.

Plug the alt harnes back in and the take the volt reg out. Might just be a bad volt reg?

Those are cheap.

I'm in Leominster.
25 min.s

unplug just the alternator at the alternator.
It may be the reverse light switch....same part of the harness and it may be the same plug.

Rich

Ok I'll pull the voltage regulater first.
Then I'll try unpluging the alt. Can I access it by hand from under the car?

not easily...but yes you can.

Chelmsford Auto Electric is where to bring it if it needs rebuilding.
Up near the tyngsboro bridge...

Rich

I just pulled out the voltage regulator from the relay board and my meter still shows a power drain.

So now I'll try disconnecting the alternator directly.

[quote name='r_towle' date='Apr 6 2011, 02:01 PM' post='1454691']
not easily...but yes you can.

How else can I do it?
Snip the wires in the engine compartment, then splice them back together when I finish checking?

Steve

well, that might seem easier, but it wont be in the long run.
Jack her up and climb underneath....

Rich

Spoken like an old pro. We can sit here and talk all day or we can climb under and do it in a few. The voice of experience is the wise teacher.

The alt harness unplugs from the relay board ............ the hot wire to the alt is on the same terminal on the starter solenoid as the feed to the starter from the battery.

Hi Ron;
Are you saying I can just loosten the nut on the starter solonioid and take that hot wire off?

Rather than pulling apart the sheet metal to get at the alternator, I disconnected the red hot wire that was attached to the starter solonoid (and positive battery lead).
My multimeter dropped to zero. Is this now telling me that the alt. was the parasite?
And if so, should I have mine rebuilt or just source a new one?

yes the diodes are blown and it needs to be rebuilt. [diodes are like a one way valve to electricity]

yes the diodes are blown and it needs to be rebuilt. [diodes are like a one way valve to electricity]
[/quote]


Alrighty.
When I jump the car and have it running, my multimeter shows that the alternator is charging the battery, though. Would it still work that way if the diodes were shot?

[quote name='moneysmarts' date='Apr 6 2011, 06:05 PM' post='1454764']
yes the diodes are blown and it needs to be rebuilt. [diodes are like a one way valve to electricity]
[/quote]


Alrighty.
When I jump the car and have it running, my multimeter shows that the alternator is charging the battery, though. Would it still work that way if the diodes were shot?
[/quote]
yah, for a while, it's going to over load the ones that are still working and blow all of them.

it won't be making the full rated output in current.

the diodes convert the a/c that the "alternator" makes into d/c, by taking voltage at 180 phases ...... well it gets complicated to explain in text and is easier to do on a chalk board.

look it up here http://en.wikipedia.org/wiki/Rectifier

OK
Thanks much.
I'll have to pull it out tomorrow.

Troy is my hero.

I would agree with Troy's assesment also, but there could be something else going on in the alternator. The brushes wear down coating the inside with carbon dust. If your engine is an oily one, the oil vapors and carbon dust can combine to make a" resistor". If this "resistor" happens to be across one of the diodes, it can cause a drain across it and still allow the diode to assist in the charging process.
I recently had a similar problem on my Dodge truck where it was not charging properly. Took it off to inspect and the carbon brushes were almost gone and the dust was so thick and oily that it was preventing the alt from charging correctly. Just cleaned it up, blew it out, and put in new brushes and all it back to like new.
http://www.ephotomotion.com/914engine/alt1.html
This website ahs a detailed process on what to do for your alt.
Tom

in my recent experience with bosch rebuilt alternators, I would suggest you bring it up to Chelmsford auto electric and have them rebuild it for you.
Its cheaper and it will last a good long time.


Rich

Rich:
I dropped the alt. off to Brian this morning at Chelmsford auto electric.
He just called me and said they cleaned it up, and replaced the bearings (for $65) but that the diodes were fine. They were not drawing any amps!
When I pick it up tomorrow, I'm gonna bring in my voltage regulator for him to test. But I'm reasonably sure that's not the parasite.

how did they test this?

did they test each of the six diodes? or just check to see if it was producing a charge? it will still produce a charge if a couple of diode are shorted but will not provide full current charge. [amperage]

I have no idea Troy.
When the guy called me and said it was ready to be picked up, I asked him if the diodes were gone. He said they checked out fine.
I told him I had a voltage leak, and described my tests, but he insisted they were ok. Just cleaned the brushes, and changed the bearing.

troy, these guys are very good.
This is all they do...never ever ever had a problem.
All they do is rebuild elec motors etc...
They rewind them in house...they know what they are doing.

Rich

well then i guess you can throw it back in and see what happens.
it might be as tom says that cleaning it up will cure it.

before you pick it up i would ask them what test they do to analyze the output capacity of the alt. and if they check dc voltage ripple this will tell them if the rectifiers are bad [high ripple means bad rectifier]

OK, can someone post a diagram of that little wiring section?
Alternator, starter circuit and maybe....reverse light switch?

Is that all using the same plug?

Rich

Rich:
Just to refresh what I did...
When I pulled the 3-wire alt. plug from the relay tray, my amp draw stopped.
The I reinserted the plug, and disconnected the hot wire from the alt (attached to the starter solonoid). That also made my amp draw go away.
Should I do some other tests?

just wondering if they threw it on the bench and it threw out some current and assumed good to go.

put it back in...unplug the lead at the starter solenoid.
Also, do you have the logic circuit (looks like a relay) under the passenger seat?
Two big yellow wires (yellow and yellow with red stripe)

And , where oh where does the reverse light switch get its power from?
Seems like it may be part of that hot lead...its in the same area.
Reverse light switch gets stuck...power draw....dunno.

Rich

reverse light is switched on the key on can't be that.

inspect the wire from the alt to the starter, could be damaged just bad enough to allow a small high resistance short, corrosion can cause high resistance shorts [draws] that when cleaned up resolve issues.

It looks ok, but I can replace it.
Any special gauge I should use?
Braided or solid?

Backup lights ... fuse 8 or 9? .... thru the main harness (pins 3 & 4 on 14 pin connector) to relay board ... thru the relay board (pins 2 & 4 on 12 pin engine harness) to engine harness which contains the two wires to switch on tranny.

there are no abrasions in the wire jacket? then it should be fine. the condition of the ends of the wire at the connectors, if the wire has broken strands replace the connectors.

i'm not sure what ga wire is run from the alt to the starter but 8-10 ga should be good. [prolly over kill for the short run].

how are you testing for draw? where are you doing the amp draw test at?

nothing on the relay board get constant hot with the key off. the draw is not comming thru this current path.

The question was "Where oh where does the backup lights get power?". No reference to the power drain.

how are you testing for draw? where are you doing the amp draw test at?
[/quote]


I've disconnected the positive battery cable and have connected the multimeter between the battery post terminal and the cable.

so when you diconnect the wire from the alt to the starter the draws stops, and when you pull the alt plug from the relay board the draw stops. it points to the alt as the only suspect.

Yup.
Quirky.
I'll put it all back together tomorrow night and see what happens.
Thanks for brainstorming.

I''l bet them cleaning it up cured your drain.
Tom

I'm curious what it is
Keep us posted.

I have been tied up all day.
I'm going to have at it tonight.
I'll post the results.

OK Here's the update.
When I picked up the alt at the shop, the guys there told me they saw no electric draw. I explained to them in detail how I narrowed down the source to the alternator. They rechecked the diodes, and decided, even though they worked fine, to replace three of them.
I brought it home and got it all back together.
And according to my multimeter, the drain is gone.
After my car sat in the garage all night, it fired up this morning, no problem at all!
So I guess I have no idea what cured it, the cleaning or the dioides, but it works for now.
Thanks for all the help trying to figure this one out.