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Keep killing alternators, A15 motor in an MG


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O'Reilly remanufactured 65 amp alternators.

I have the two wire connector, the hot +12V lead and the wire that goes from a spade lug to the distributer.

My battery was going dead, but I just put this battery in brand new a week ago.

The problem wasn't happening before getting the new battery, the old one turned 7 years old so I replaced it.

 

I put my meter between the battery negative post and ground (disconnected first) to read current draw.

Read 2.5 Amps with everything turned off.

Pulled fuses one by one, no change.

Pulled the two wire connector from the back of the alternator, dropped to zero Amps draw.

Sounds like blown diodes in the alternator.

What can cause it, what can I do about it?

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Often the reman alternators are crap right out of the box. Keep returning them until you get a good one.

Yes, this so much! I'm on my third O'Reilly alternator in the last 3 years. The lifetime warranty takes the pain out of it but it still sucks having to screw around. They will test them in store for you, they can still test good but take a listen as they test and play with the alt to look for bearing slop. I had them run through a batch until I got 2 good ones, one to put on the car and a good spare.

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That has been my experience too, I just got this one in January it's lasted the least of any I have gotten from them.

I started thinking I'm doing something wrong.

It is charging at 14.7 and that seems a bit on the high side and like I said drawing 2.5 amps whenever the connector is plugged in.

Could replacing the battery blow out the diode? I assume that is what's happened here why it's drawing 2.5 amps.

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Can't see how. Batteries are about 12.3 volts fully charged. Alternators make 14 to 15 volts output. They are simply a crappy Asian rebuild. A new Nissan alternator is close to $300, no wonder they last the life of the vehicle and even then probably only need new brushes.

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I have the two wire connector, the hot +12V lead and the wire that goes from a spade lug to the distributer.

The E terminal should go to Earth/Ground and be bolted (not a spade terminal, which corrode over time). The distributor body is a ground, but not a reliable one. I would ground it to the timing cover bolt like Nissan did.

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Strange stuff.
I took the alternator in and they tested it ans said it was bad.
I eventually got a new one and brought it home and installed it.

Started the car and it ran great and the charging was at 14.3 VDC.

I turned it off, pulled the negative cable from the batery and measured draw.

2.5 Amps

Threw up my hands and gave up.

Pulled a toggle switch and some wire and ran it to the alternator and installed a bypass.
The "top" wire had no impact on disconnection.
The bottom wire (of the two wire plug) had the effect of making the current draw zero when disconnecting.
I put my toggle switch on this wire.

The wierd part:
When the toggle is off the car starts fine and the charging of the battery is at 14.3VDC.
The current draw is zero when the car is turned off.
 

The second wire of the two wire plug draws 2.5 amps with the toggle on.

 

The second wire is not needed?

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MG Midget

It has functioned pretty much correctly for the past 7 years, not sure what has changed.

The way I understand it is:

L goes to the charging lamp, red light on dash

Start car, lamp goes on, excites circuit in alternator to switch charging on, lamp goes out

 

What is the function of S?

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Maybe you accidentally were switched from external to internal alts.??? Or the other way round. '78 and up were internal on all Nissans. I don't know what set up you have on an MG... probably an external voltage regulator?

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Maybe you accidentally were switched from external to internal alts.??? Or the other way round. '78 and up were internal on all Nissans. I don't know what set up you have on an MG... probably an external voltage regulator?

 

 

If you still have the Lucas electrical system in your Midget/Sprite, you are in for a really frustrating ride.  Good luck.

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I can vouch for the cheap alternators, too.  While it could possibly be something else. I have never had any luck with orielly or autozone alternators.

 

I spend the extra few bucks at NAPA auto parts and use theirs. Over priced, probably.  But I install and forget about it.  Hell they probably in 5 cars while in my hands with the way I go thru cars :rofl:

 

 

Check the part numbers between napa and autozone and who the mfr is. often if the same mfr i can get them to lower the price, even tho they use higher quality parts for the reman at napa.

 

You could take it to a reputable shop and have it rebuilt right on the spot to your specs with higher grade parts.

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The ignition switch is for the MG, I have replaced a lot of the other parts.

It's a 78, they came with internal regulator alternators.

 

O'reillys wanted to charge me $87 for this alternator, I told them nope - warranty replacement.

That's when he took the old one back to test it, came up and said it didn't pass and handed me the new one.

 

I doubt he knew what he was doing and finally just opted to believe the customer since this new one acts just the same as the old one did.

 

Anyway, from the diagram above it looks like the S wire can be jumpered to B.

Then I only have to be concerned with the L circuit.

 

I'll make sure that goes to the lamp and the lamp comes on when I turn the ignition switch on then the lamp should go out once the alternator gets "excited".

If the lamp does not go off then that means the alternator or the ignition is feeding power to the lamp - easy process of elimination.

Maybe no easy solution, but it should be easy to figure out which one is feeding power to the lamp.

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L is lamp.

S is sense.

 

It doesn't work like old alternators. L is an on/off switch for the lamp.

 

If the lamp does not go off then that means the alternator or the ignition is feeding power to the lamp

Except the light is already connected to power via the car's instrument panel harness.
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The S is your voltage sense circuit.  It's the voltage the alt reads to determine output.  Connecting it directly to the alt positive output or even the battery can give you undesirably low voltage output.  It's better to have it connected farther away where it can detect voltage drop and increase output accordingly.

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The S is your voltage sense circuit.  It's the voltage the alt reads to determine output.  Connecting it directly to the alt positive output or even the battery can give you undesirably low voltage output.  It's better to have it connected farther away where it can detect voltage drop and increase output accordingly.

 

That makes 'sense' to me.

I am about to the place where I get a little free time to go out and look at this again, so I will check it all out and come back with what I find.

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Wrong. Datsun connected it directly to the fusible link. Check the factory service manual.

 

All right, well I don't seem to have a fusible link so what's a suitable different place to connect this?

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Wrong. Datsun connected it directly to the fusible link. Check the factory service manual.

 

What's wrong?  Don't get me started on all the "wrong" electrical that Nissan did at the factory.

 

Edit: Not to say that I don't think connecting to the battery positive isn't fine, it is.  I was more talking about jumping straight to the alt output, which people do when trying to create a one wire alt...

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