Blowing alternators - positive diode

[Guest BuickWildcat401]

Guys,

I bought a '73 Riviera a couple of months ago and have begun serious renovation.

All has gone well until recently and I'd like some advice if you can give it.

The car had a new but very small battery and the generator light would come on and off when the engine was running.

Testing the charging system I found 14v and thought the batt must be the problem. Replaced the batt with an appropriate one.

Started the engine and no generator light. All was great until I turned the engine off and the generator light was the on!

I removed the key and it was still on. Checking the book I found this was a blown positive diode in the alternator.

I installed a new alternator, thought I found a problem with a loose connector to the alternator and replaced it. Even before I started the engine but connected the negative cable to the batt, the generator light came on - engine off.

I ran the engine (generator light off), turned off the engine and generator light on.

I have to disconnect the batt to keep the light off now.

Bought another alternator. Tested wires to blower. Found frayed wires and repaired. Disconnected all connections to blower, relay, resistor, ambient air switch and even the belt on the air compressor. BLEW ANOTHER ALTERNATOR. I know these are cheap, Mexican rebuilds but THREE!?

Checking the batt cable to starter solenoid and batt ground all look good.

There must be a short to ground in the electrical system somewhere - right? Even without the ignition system the alternators are blowing the positive diode. I must be missing something somewhere.

Okay, has anyone had this problem or does anyone have a good idea where the problem might be?

Thanks Boys and Have A Great Weekend.

Mike

mmanguno@hotmail.com<!-- google_ad_section_end -->

[Guest BuickWildcat401]

Guys,

I bought a '73 Riviera a couple of months ago and have begun serious renovation.

All has gone well until recently and I'd like some advice if you can give it.

The car had a new but very small battery and the generator light would come on and off when the engine was running.

Testing the charging system I found 14v and thought the batt must be the problem. Replaced the batt with an appropriate one.

Started the engine and no generator light. All was great until I turned the engine off and the generator light was the on!

I removed the key and it was still on. Checking the book I found this was a blown positive diode in the alternator.

I installed a new alternator, thought I found a problem with a loose connector to the alternator and replaced it. Even before I started the engine but connected the negative cable to the batt, the generator light came on - engine off.

I ran the engine (generator light off), turned off the engine and generator light on.

I have to disconnect the batt to keep the light off now.

Bought another alternator. Tested wires to blower. Found frayed wires and repaired. Disconnected all connections to blower, relay, resistor, ambient air switch and even the belt on the air compressor. BLEW ANOTHER ALTERNATOR. I know these are cheap, Mexican rebuilds but THREE!?

Checking the batt cable to starter solenoid and batt ground all look good.

There must be a short to ground in the electrical system somewhere - right? Even without the ignition system the alternators are blowing the positive diode. I must be missing something somewhere.

Okay, has anyone had this problem or does anyone have a good idea where the problem might be?

Thanks Boys and Have A Great Weekend.

Mike

mmanguno@hotmail.com<!-- google_ad_section_end -->

Hello?

Anyone there?

You mean none of you have ever had this problem?

Ok, thanks anyway.

Mike

[1965rivgs]

Hi Mike,

Sounds like you are assuming, due to the gen light, the positive diode has blown in all three alternators. Is it possible the gen light comes on when the key is off for some other reason other than the alternator? Like some creative wiring somewhere under the dash, like an obsolete radio feed, which is simulating a "key on" condition by backfeeding the ignition switch? I have found this to be the case several times.

Tom Mooney

[Guest BuickWildcat401]

Thanks for the tip Tom. I will check it out for sure. At first thought I am doubting that is the case because two of the blown alts were bench tested and the diode test failed (the third blown alt is still on the car). Of course, Pep Boys is doing the alt bench test so who knows for sure if they are actually blown right?

When I bought the car the generator light flashed on and off while the engine was running (no generator light when off). After replacing the very small battery it ran without the generator light flashing. I thought everything was fine until I keyed off and got a generator light - even with the key out.

I have voltage drop tested the positive and negative sides of the circuit, resistence checked every wire, unplugged the blower, resistor and air ambient switch and still blew the third alt. It is frustrating to say the least. But I have not yet looked behind the dash as you suggest. It's worth a try at least and I appreciate your input. Interesting that you've run into that kind of situation before but I guess nothing is surprising with a car that's old.

[alini]

Disconnect the alternator completely (protect wires from grounding) and then hook up the battery. Does the light still come on>? If so, the Alternator is removed from the system and its something in the wiring.

[Guest BuickWildcat401]

Thanks alini. No, the light does not come on. This confirms the alternator positive diode(s) is / are shorted. So I've confirmed the alternators have been shorted but still do not know what is doing it. The research I've done indicates this kind of problem is typically on the positive side of the circuit and to perform a voltage drop test. I have done both sides and found no dropped voltage. I've checked resistance in all wires and cleaned the contacts. I repaired some frayed wires I found and replaced a connector. I must admit a couple of these things were done after this third alt was installed so it is possible I repaired the problem but I fear blowing another (4th) alt and another $50.00.

Any suggestions for taking any readings before I buy another alt and install? I wish there was a way to know if the circuit is good beforehand. Am I missing something?

Thanks,

Mike

[alini]

Knowing that its in the alternator somewhere, that narrows down the wires involved. Check your wiring from the Alternator back. Check for loose connections, check your mounting bracket too, see if somethings loose or arcing. I dont have a wiring diagram for that year so I cant give you actual wires to check, sorry

[alini]

Instead of replacing the alternator have you checked with local vendors who can rebuild your existing one. Replacing diodes has to be cheaper than replacing the alternator

[Guest BuickWildcat401]

Instead of replacing the alternator have you checked with local vendors who can rebuild your existing one. Replacing diodes has to be cheaper than replacing the alternator

Thanks for your advice on this. I actually tried to do just that but how the heck do you keep the magnets in their slots when putting the casing back together? The springs push them out. I'm sure there's a way to do it. You are absolutely correct that it would save me alot of money and time.

Thanks Again,

Mike

[alini]

There is a small hole that goes through that case, and a correspnding hole in the back of the alternator case....stick a piece of coat hangar through there to keep the magnets back. once its all assembled, remove the wire

[steelman]

A coat hanger is too big around. A piece of welding wire or a stretched out paperclip is about right. You can use a toothpick in a pinch.

[Guest BuickWildcat401]

Great advice on alt reassembly. Many tks. U guys just saved me a bundle. I'll let u know how things go once I return from vacation & work on my midnight blue riv baby again.

Mike

[Guest BuickWildcat401]

Okay Boys I am Back!

After reorganizing from vacation return I got to work again on my RIV.

I replaced the positive diodes after cleaning all contact points, checking all resistance in wires on both positive and negitive sides and a general going over of the charging and starter system. I found no wiring problems after my repairs. I replaced the diodes in the alternator (thanks) but they blew again......!

Okay, now I decided to sit back and rethink................. When I bought this baby the alt was flashing on and off so I knew there was a batt, alt or wiring problem. I tested every damn wire, replaced the alt 3 times / rebuilt the last one myself with advice from this great forum - but blew it too!

Now...............they say you miss the obvious first. I hope that is true because the new batt I bought is DOUBLE the CCA (cold cranking amps) of spec. Certianly this could knock out the diodes in the alt. (Buying a '73 Riveria Shop Manual is priceless !).

[Guest BuickWildcat401]

But if any you boys read and think something differently please let me know.

Thanks again to all and I will certainly keep you informed of what happens and the eventual success of this "Last Year - One Year Body Style' Boat Tail Riviera.

Mike

[Guest BuickWildcat401]

Crap. Now the alt checks out okay (no blown diodes) but the generator light is still on with the ignition in the "off" position (or key removed for that matter).

I checked grounding from the alt housing to the block and get .2 ohms so that is good.

At this point I can only think there is a closed circuit when the ignition switch is in the off position. That would lead possibly to the resistor between the switch, generator light bulb and alt. I'm guessing it's on the printed circuit sheet on the back of the instrument cluster. Any of you guys ever have this problem?

Thanks again,

Mike

Edited July 25, 2012 by BuickWildcat401
left out a word (see edit history)

[1965rivgs]

Hi Mike,

See my above post, #3. You most likely have something seeking ground and it is finding it thru the gen light. Look for something that is not working (due to insufficient ground) and you will find your culprit.

Tom Mooney

[Guest BuickWildcat401]

Tks Tom

I will look for grounded wires. I have so many things disconnected its gonna take time but I'm in no rush.

[1965rivgs]

No, not grounded wires or shorts (except for below). You are looking for a component, dash light, courtesy light, glovebox light, etc, that is not functioning due to an open or no ground where there should be a ground. The non-op component will seek ground wherever it can be found. If you have many things disconnected that could produce stray voltage seeking ground. Do all the dash lights work? Something in close proximity to the gen light may be seeking ground.

You may also have two circuits which are shorted into one another although this is less likely. Like a hot wire on one circuit which has rubbed into the gen light circuit and is sending voltage thru the bulb to ground. Have a helper watch the gen light and do a "wiggle test" on the wiring harness under the hood and/or behind the dash. If the light goes out or flickers you can at least pin down an area.

I had a similar occurance on a `62 Starfire ..a wire rubbed thru on a male terminal in the back of the fuse box. Left me stranded but I managed to fix it in the parking lot at work, it was my everyday driver and I couldnt afford a tow! Ahhh...the good old days...good luck,

Tom Mooney

[alini]

Have you changed the voltage regulator on the fender well yet??

edit: sorry forgot you are working on a 73. does it have an external regulator?? Not sure which year they went internal regulators. There really isnt alot to the system regardless of year, so Im puzzled how nothing has been found yet

Edited July 26, 2012 by alini (see edit history)

[Guest BuickWildcat401]

No, not grounded wires or shorts (except for below). You are looking for a component, dash light, courtesy light, glovebox light, etc, that is not functioning due to an open or no ground where there should be a ground. The non-op component will seek ground wherever it can be found. If you have many things disconnected that could produce stray voltage seeking ground. Do all the dash lights work? Something in close proximity to the gen light may be seeking ground.

You may also have two circuits which are shorted into one another although this is less likely. Like a hot wire on one circuit which has rubbed into the gen light circuit and is sending voltage thru the bulb to ground. Have a helper watch the gen light and do a "wiggle test" on the wiring harness under the hood and/or behind the dash. If the light goes out or flickers you can at least pin down an area.

I had a similar occurance on a `62 Starfire ..a wire rubbed thru on a male terminal in the back of the fuse box. Left me stranded but I managed to fix it in the parking lot at work, it was my everyday driver and I couldnt afford a tow! Ahhh...the good old days...good luck,

Tom Mooney

Thanks Tom. Everything works electrically on the car. Quite amazing actually - even the rear window defogger motor and trunk release! I get your point though about a component. When I first got the car the batt was tiny - the guy put one in cheap enough to start it I guess. The generator light continuously flashed on and off with engine running. No gen light when ignition was off. When I changed the batt the generator light went out when running but I was very surprised to see it when I turned engine off and took key off. I am thinking it may be in the dash - possibly the resistor. There is a dual switch resistor that is attached to the ignition switch which is wired to the alt and bulb. I am guessing it is on the plastic printed circuit board behind the generator panel but will check.

Thanks again and I'll let you guys know what happens.

Mike

[Guest BuickWildcat401]

Internal regulator. Checked out (passed) on test bench.

Usually these things are obvious but sometimes ya gotta go deeper and I am thinking it's behind the dash. Fortunately the wiring is almost virgin with very little hacking.

Thanks,

Mike

[Guest BuickWildcat401]

Ok Boys I finally corrected the problem and you won't believe what it was.

A guy that owns his own shop advised me that many rebuilt alternators are done incorrectly.

On the rebuild line parts are often left off. All the alts I bought were from Pep Boys and all rebuilt in Mexico.

There is a small cover that should be placed over the internal regulator. If left off it may not matter in many cars but in others it will send a low voltage signal (engine off) that illuminates the generator bulb in the cluster panel.

I went through three Pep Boys alternators and they all had this condition. The shop owner got a reliable one (he used to have an alt rebuild shop) from a trusted source, installed it and the problem is gone.

Amazing - I would never have thought of this possibility but hopefully this will help someone else who has had the same problem.

Thanks for your assistance guys.

Mike

[alini]

Glad you found a solution and mental note made about alternator quality.

Thanks for the update