The Stovebolt Site Forums The Shop Area The Electrical Bay alternator wont charge

Hi Guys, I installed an alternator yesterday in my 55.1st series. I used an alternator from the junkyard and followed the directions in the tech tips here. The alternator I have has a two pronge connector, and a Batt. terminal. I connected the heavy guage (10)wire to the existing wire in the trucks harness that went to the Batt. terminal on the reg. and the lighter guage (12)wire to the 12v supply to the coil. Fired the truck and the all was fine the alt was showing a charge. When I went to turn it off the truck would not shut down. I had to stall the engine. On the next start up it was not showing a charge and when I pull the ground wire it shuts down.I cant measure a charge from the heavy wire form the alternator any more but from the Batt. terminal on the alternator (whic is not connected to anything) it shows 25v. Where did I go wrong.Or is it just a bad part.

Thanks
Tony

Wire to the coil? I never heard of hooking a wire to the coil. I think (but I have not read the info in the tech tips)that the wire you have hooked to the coil should be hooked to the ignition switch and the other small sire is hooked to an idiot lamp. I am gonna go look at that tech tip.

The wire that carries power to the coil is from the ignition switch and is 12v switched. I should have been more clear but wanted to keep it short.

OK Tony I read the tech tip. Still don't like the idea of hooking up the alt. to the coil positive. Seems to me if you have a bad diode in the alternator it would continue to excite the coil and wouldn't turn off. Hey it was doing that wasn't it. Tony you may have a bad diode trio in the alternator.
You may want to remove the alternator and have it tested before you go any further.

Its been a long time since I took apart an alt. but its not realy that hard to do. The hardest part is when putting it back together you need to put the brushes back in thier place and secure them there with a paperclip. The factory left you a hole to do this with on the back of the alternator. Just straighten out a paper clip and while holding the brushed all the way in push the paper clip throught the hole and over the top of both brushes, put the back of the alternator on and then remove the paper clip.

I see what realy needs to be done to avoid engine run with a bad diode but it requires replacement of the ignition switch to one that has 2 separate hot lugs when switched on.

What did you do with the 3rd wire off the alternator?

Tony,

Your part may be BAD now! I'm not clear from the information you have posted, but will mention a few thoughts/questions.

There are several alternators that look similar, but are different..one is used with external regulator, the kind on the firewall. The other kind, which is more modern, has a internal regulator.

In lieu of a part number, the 'two prongs' would be the giveaway.

If the 'prongs' resemble this..II..the alternator requires a external regulator.

If the 'prongs' look like this..- -..It is a SI style and has a internal regulator.

To start with, you need to figure out which one you have. The hook up similar, except one needs a compatible regulator.

Your wiring description above didn't mention a third wire...where did it go.

Find out which alternator you have and many folks will jump in and help. This is a constant subject of discussion here.

The common name for the 'prongs' is a DA plug.

Stuart

Oh if you decide to do the repair yourself, mark the rear housing of the alternator. Use a sharpie and make a straight line from the pulley end to the wire end of the alternator. It needs to be clocked (lined up)properly to work. That rear housing will go back on 4 ways and only one way will work.

The prongs lay flat - - . There is nothing attached to the Batt. terminal on the back of the alternator, however that is where I am able to measure 25v now.

atomarc, after reading his post again I think he may have grounded that 3rd wire, in doing so could have shorted out the diode assembly. That 3rd wire is to excite the idiot lamp when not charging. exp; Key on engine not running lamp on. Some GM's would not charge with out a bulb in the socket or a burned out bulb.

Toyvo, You mentioned a diode in the 12v supply to the coil. Is this the same as a ballast resister that is mentioned in the instructions to convert to 12v alternator. If so and if that could cause this failure then thats it as I did not install this part because this truck was allready 12v generator (That was nonfuctional)whenI started I did not think it was nessesary.

You guys paying attention????

The wiring below is how it should be wired and coincidentally is how GM wired them.

Directions that include, moving the second wire on the thing-a-ma-jig over to the post on the do-hickey, usually end in failure.

The resistor (10ohm,10watt) and the bulb can be tied together and connected to a single ign switch contact. The bulb can even be eliminated, if you choose.


[img]http://www.rowand.net/Shop/Tech/images/AlternatorWiringOverview-1973to1985Buick.jpg[/img]

I should like to add this.
Some people will tell you that you don't need the resistor. Some people will tell you to simply run a wire from the #2 on the Alt, directly to the BAT terminal. Some people will say to put a diode between the #2 and the BAT.
They usually end up with an Alt that won't start charging until they rev the engine to 1500 rpm. They accept that.
Wire it right and it will work right.

Richard that is what I thought, somthing had to be done with that extra wire and I could not remember what. It could also be used to excite an idiot lamp if one chose to do so.
I would suggest running the excite wire to the switch at a differant (on hot) lead than the ignition. I realy think he has blown a diode and is now back feeding the coil from the alternator, and that is why it would not turn off.
The diode trio assy. is inside the alt. Tony one of the diodes is probably blown.

Richard,

It must be male PMS. Everyone on this forum is on a different technical level.

Everyone that posts on this forum is here because they need help, or want to share knowledge and give help.

When you demean someone for lack of technical ability or improper technical jargon, it serves no positive purpose.

A post can be helpful and informative without being condescending. If the question is answered with a positive tone, it makes the job much easier.


Stuart

atomarc, I realy didn't think richard was out of line, i dont think Tony did either. Or was it me you were refering to? Anyway Richard jogged my memory some with the wiring diagram. Thanks Rich.

OK guys it looks to me as though I need to loop the batt. terminal into the #2 terminal and add the resister and light bulb into the line marked #1 rebuild the alternator and put some heat to her. Hopefully not to much heat. Like always Thanks for all the help. I'll let you know if it works or burns to the ground. And by the way that reminds me to say Thanks for the info last week on the oil pump. I cleaned the screen an reinstalled it and all seems fine.

Thanks
Tony

Tony,

Your 55 1st won't have the idiot light.

Sometimes you can find a DA plug that has a diode incorporated into it if you are concerned with 'run-on'.

For some reason, not all installations of this type will experience run-on. Good luck

Stuart

Tony you dont have to install the resistor and the bulb either one will work alown. If you install the resistor you don't need the bulb. The resistor is there incase the bulb burns out so the system will still work. So really you dont have to put in the bulb. A bulb is nice to have tho.
Good Luck!