No alternator seems to work!

[Gibson]

Ok this problem has stumped all the car guys in my neighborhood. The fundamental issue is: no alternator (tried three) will pump out more than 12.5 volts. When not hooked to the battery main, the alternator will put out 19v-45v depending on engine RPM. We've checked a laundry list of things which I'll describe below. (sorry so long)

Its a '78 c10 with a 350 and a for a week or two it was squealing really bad and when it did, the voltage would drop down to 8 volts. So I ordered a new alternator. Before the new alternator had arrived, it made a bad squeal, then threw the belt into the fan clutch. I went and got a new alt from the local parts store and a new belt, but on testing the voltage after it was hooked up I noticed that the voltage basically didn't change when I started the truck. So I took the alt and battery to the parts store - both tested good. I checked the voltage on the leads to the alt and the primary and the post 2 (bigger red wire) have full voltage and post 1 (smaller white wire) has a few volts less which I understand is what it is suppose to have.

We got a different alternator and it was the same deal. We tried running new charge/ primary leads and and double checked the ground. I had done some painting in the engine compartment so I double checked all the grounds and cleaned them up. I pulled all the fuses too. No significant change.

I am absolutely stumped. Any help is greatly appreciated!
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[76stepsidechevy]

what happens when the battery gets down below that 12.5 volts? try levaing the lights on for a while to let the voltage drop to say 11 volts and then start the truck and watch the voltage.

[Gibson]

Originally Posted by 76stepsidechevy

what happens when the battery gets down below that 12.5 volts? try levaing the lights on for a while to let the voltage drop to say 11 volts and then start the truck and watch the voltage.

When we hooked the first replacement alternator the battery had run down a good bit from driving back. It was about 12.25. When we started it up it hopped around from the 11s on up to 12 or so, but never above the resting voltage.
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[1LowToy]

Easy to a little harder.
Disconnect the small plug on the alternator and check for voltage from the wire. Voltage from one wire is a must with key on.

Disconnect the hot lead from the alternator (Battery disconnected of course) then connect the battery again and check for voltage at the hot lead wire. No voltage bad wire (fusible link) to the starter or battery.

Would you happen to have a after market amp gauge?

[Gibson]

Originally Posted by 1LowToy

Easy to a little harder.
Disconnect the small plug on the alternator and check for voltage from the wire. Voltage from one wire is a must with key on.

Disconnect the hot lead from the alternator (Battery disconnected of course) then connect the battery again and check for voltage at the hot lead wire. No voltage bad wire (fusible link) to the starter or battery.

Would you happen to have a after market amp gauge?

No aftermarket Amp gauge, nope. Plug has full voltage on post 2, slightly lower on post 1 (exciter wire).

Do you mean to check voltage at the battery when the alternator primary is disconnected? But leave the pigtail hooked up?
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[Gibson]

I guess I should clarify that: I AM using a seperate voltmeter to check things out, but it is a stock volt gauge in my cluster.
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[Axle]

1. Don't disconnect the battery from a running vehicle. I can damage the alternator.

2. Check your grounds.
3. Don't rely on the dash guage for your readings. Verify actual battery voltage running and then see what the dash reads and make a mental note.

4. Disconnect everything on the alternator. Measure battery voltage. What do you read?
5. Measure from ground to the #2 terminal in the small pigtail. What do you read?
6. Key-on. Measure voltage from ground to terminal #1 (brown wire). What do you read?

7. Hook everything up.
8. Start truck.
9. Hook your meters ground lead to the alternator BAT terminal and Measure the voltage AT THE BATTERY positive. What do you read?
10. Measure the the voltage between the alternator case and the battery NEGATIVE. What do you read?

That'll get us started.
Does the amp light light up on the dash with the engine off, key on?

Alex.

[Gibson]

I'll try those steps tomorrow after work and post back - thanks!
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[Goldfinger]

I went through a few alternators because of the cable that connects to it was gummed up.

[Gibson]

Ok, I've done the tests Alex mentioned. I used an actual volt/ohm meter for these tests. The battery voltage with the truck off is 12.45 volts. When running, voltage at the terminals drops to 12.25 or so.

1) I made sure I did not disconnect the battery while running
2) I re-ran or thoroughly cleaned all grounds I could find (even the one next to the fuse panel under the dash)
3) I made sure to use an actual meter. The stock voltmeter shows about 10 volts when the voltmeter says 12, but I recently put a new face on it so I may have just not positioned the needle carefully enough.
4) with the alt disconnect and engine off, voltage is 12.45 (same as with it connected)
5) voltage with engine running: post 1 is 12.20 volts and post 2 is 12.25 volts. Voltage on the primary is also 12.25. Post 1 maintains this voltage constantly.

6) post 2 is jumpered to the primary about 2 feet up the line so it always reads the same as the primary (12.45 at rest, 12.25 when running)

I checked the resistance between the battery negative and alt case: 0 ohms.
I have a factory volt gauge - none of my dummy lights are for the battery (only seatbelts, choke, brake and... There was one other that I can't remember, but it wasn't electrical related)

Originally Posted by Axle

1. Don't disconnect the battery from a running vehicle. I can damage the alternator.

2. Check your grounds.
3. Don't rely on the dash guage for your readings. Verify actual battery voltage running and then see what the dash reads and make a mental note.

4. Disconnect everything on the alternator. Measure battery voltage. What do you read?
5. Measure from ground to the #2 terminal in the small pigtail. What do you read?
6. Key-on. Measure voltage from ground to terminal #1 (brown wire). What do you read?

7. Hook everything up.
8. Start truck.
9. Hook your meters ground lead to the alternator BAT terminal and Measure the voltage AT THE BATTERY positive. What do you read?
10. Measure the the voltage between the alternator case and the battery NEGATIVE. What do you read?

That'll get us started.
Does the amp light light up on the dash with the engine off, key on?

Alex.

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[bowtiemanchevyman]

what is the voltage coming out the charge back wire on the alt. when the truck is runing you should have 14.5 or 13 voltage if it is 12.5 at the back of the alt. something is wrong with the alt. on my truck the red wire goes to the back of the alt. so that when the truck run the alt. get power and only when the truck runs. and the charge back wire run to a block on the fire wall where it goes to the starter and to the fuse box. to power your truck. the other wire goes to your gauge. and it is a groud wire for the gauge. so you need to check all you wiring for that Circuit. what amp is that alt.? if its more them 65 amp you will have to change the charge back wire to a bigger wire to carry the higher amp. and just because you bought a new alt and tested at the store dont mean is good i use to wrk at one of those place and they dont know that much about cars. if all you get is 12.5 volt even when you rev up the motor to 3000 RPM and dont change something is wronge with the regulater its not letting it charge up where its suppose to be.

[Gibson]

Originally Posted by bowtiemanchevyman

what is the voltage coming out the charge back wire on the alt. when the truck is runing you should have 14.5 or 13 voltage if it is 12.5 at the back of the alt. something is wrong with the alt.

It is 12.5 - BUT I am positive that the alt and battery are ok. I have tried 2 different alts from two different manfacturers (both right out of the box). Both alts were tested at the store. As was the battery which is new from Napa AND tested seperatly at Advance Auto. When the alt is completely disconnected electrically from the system it puts out 19-40 volts depending on engine RPM.
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[bowtiemanchevyman]

if it is put that much out its not working right it should only put out 14.5 at the most. and like i said befor new part dont mean it is good they can get broke in travel and people at those store know what the equiment tells them not what really the part should be doing

[motornut]

just throwin this in but, did your truck come with gauges?

[Gibson]

Originally Posted by bowtiemanchevyman

if it is put that much out its not working right it should only put out 14.5 at the most. and like i said befor new part dont mean it is good they can get broke in travel and people at those store know what the equiment tells them not what really the part should be doing

It ONLY puts out that much when it is spinning free and not hooked to anything. As soon as you hook it up, it returns to not putting out anything measurable.

I suspected the alt first naturally because I've gotten plenty of brand new parts that were bricked right out of the box. I've gone through TWO though - and both tested ok at the store. But I actually have a THIRD new alt (chrome one from DB). I'll try installing it tomorrow and see what happens. I think that is the only thing left to try at this point!
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[Gibson]

Originally Posted by motornut

just throwin this in but, did your truck come with gauges?

It did come with the voltmeter, yes. I've done a lot of work to the cluster but I did not augment the volt gauge other than to give it a new face.
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[bowtiemanchevyman]

Gauge no gauge it dont matter if he has evry thing unhook and it is putting 19-40 something volts it has a bad voltage regularter. a alt. should never be more then 14.5 volt with nothing hook up and at 3000 RPM with everything hook up it should be 14.5 at idle it shoul be 12.5 -13 volts it not the alt is bad.

[Gibson]

Originally Posted by bowtiemanchevyman

Gauge no gauge it dont matter if he has evry thing unhook and it is putting 19-40 something volts it has a bad voltage regularter. a alt. should never be more then 14.5 volt with nothing hook up and at 3000 RPM with everything hook up it should be 14.5 at idle it shoul be 12.5 -13 volts it not the alt is bad.

I'm gonna kick myself if I got TWO bad alts and never tried the third. I'll throw it in tomorrow when I get back to the truck and see what happens!
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[bowtiemanchevyman]

is this a daily driver. if it is i would never put a chrome alt. on it will get hotter and wear out faster go with a polished alt. chrome holds in to much heat if i was you i would just go get a book on alt. and test your other one and rebuild it then u can paint it or polish it your self

[motornut]

the reason i asked was i just changed from idiots to "factory tach and gauges"
,had to repin the cluster
but i didn't hook up the brown wire back there(cluster)
I used the orange wire which read slightly higher on the volt gauge
i thought it might be over charging ,but it's not
wasn't sure if that could be something to check
does everything else work ok
if your worried about grounds check back there an add some for the cluster

[bowtiemanchevyman]

doing what u did wouldnt make the alt. do what it is doing the reason it is doing that is because the regulater is bad or something else in side of it not the wiring out side 19 v is alot for 12 system with its should me making 14.5 volts. not wiring it up right wouldnt cause that it would cause eletrical fire or burn up a alt. not make run like that, and to make it drop from 19 to 12 that alot of voltage drop that means the alt. cant handle a load and the winding or stater is bad which means new one not rebuilt total new/ and not chrome that is the worst thing u can do to a eletrical part. it hold in so much heat and heat is bad for ele. parts like i said be for polish or paint is the way to go.

[motornut]

Doing what I did?
So if it was wired wrong ,say with a short to ground ,that's ok?
Which would have happened in my cluster had I not repinned it.
You may think they are bad out of the box.one maybe but when your up to two/three I,d wonder.
In My case my Burb got a new alt , only to have it die on the road.
It was a short at the hitch wireing,only shorted when the lights went on

My friends dad always said "chrome don't get ya home,but it sure looks purdy when yer pushin."
Does everything else work ok?...
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[bowtiemanchevyman]

but he was saying with nothing hook up it made 19 to 40 something volts thats not a wiring problem on the out side of it. its something wrong inside of the alt. so your wiring problem would not have cause his thing no matter what.

[Junqueboi]

Sometimes the "exciter" wire is the issue. It's the smaller (brown) of the two wires in that plastic connector that snaps into the alternator casing.


Try this: while the engine is running, jump the two wires in that plug together (the red & the brown). A paperclip works perfect for this. In many cases, the alternator will "turn on" & start charging. You'll know immediately if/when it turns on.. it'll pull the RPM down just a smidge & you'll hear actually hear a very faint whine from the alternator.

TMI dept:
Many times alternator "failures" occur when the owner switches from idiot lights to gauges. The alternator light is wired in series with the exciter wire on trucks with base instrument clusters and is a necessary part of the charging system. Gauge-equipped trucks have a "special" resistance wire going to the exciter terminal on the alternator since there's no bulb.

[Gibson]

If you're ever in my neck of the woods bowtiemanchevyman, I'll buy you your beverage of choice.

I wouldn't have tried that third alternator, but did because of what you mentioned about the 19-40 volts being something that should NEVER happen. I put in my new DB alt and it started charging right away! After idling for 15 minutes or so it was reading a strong 13.5. It has a bit of bearing noise though, so I'm going to see if they will send me a new one.

I found out today when I went to return the alt that wasn't working that the lady had given me a "self exciting" alt. It has the same plugs as my old alt, but it has a cheap plastic fan (I can't even find the thing on their website). So I think what happened is when I took the FIRST bad alt back that the second one she gave me wasn't even appropriate for my truck. I don't know what would be different, but that is all I can come up with.

Thank you guys for all your help!