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Discussion Starter #1
Not my boat but my sons truck and it's got me stumped.

85 Chev 1/2 ton with a small block. Ran perfect when he parked it.

No start yesterday and we found the fuseable link was gone on the firewall. I had one of those marine style 30amp inlines so we threw that on there for grins and no problem. Truck fired right up.

He got as far as the gas station and noticed the radio had quit working. Shut the motor off at the station and no start. It had blown the 30amp fuse.

Plugged in another one and brought it home.

With a fuse in it the radio is dependent on the rpms. Let off the gas and the radio works. Give it gas and it stops. Shut the truck off and it'll blow the 30amp fuse.

I also noticed that when the radio quit the stock volt gauge would peg.

I disconnected the alternator from the truck at the main post and found that everything works perfect. No blowing fuses, radio is perfect and all is well.

On a whim I threw my digital voltmeter on the alternator main post (while it's still disconnected) with the truck running and found 34.3 volts coming off of it.

I thought to myself "self, the regulator must be gone on this alternator" so I slapped on a used one I had in the shop and tada, same exact thing.

Does anybody have any thoughts or ideas? I'm all ears.........thanks...john
 

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Sounds like something is amiss on the two wire plug on the side....This is the voltage signal that controls the alternator..If this voltage signal is low, the alternator will full field to try and build it back up...Check to make sure (engine off, key on) you have voltage going to the larger wire on the alternator lug (disconnected from the alt.), if not, hunt it down and repair it..Probably a corroded terminal in the main terminal block or something.

Good luck!;)
 

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Discussion Starter #3
Thanks Glenn.

With the mail wire that attaches to the lug on the back of tha alternator disconnected, I have full battery voltage to that wire terminal. That is the wire that returns from where the fuseable link attached on the firewall.

The #2 terminal on the side of the alternator comes up from the starter post. It has full battery voltage.

The #1 terminal on the side of the alternator runs through the firewall and disappears into a maze of wires. With the key OFF, this appears to be grounded. With the key on, it shows battery voltage.
 

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Thanks Glenn.

With the mail wire that attaches to the lug on the back of tha alternator disconnected, I have full battery voltage to that wire terminal. That is the wire that returns from where the fuseable link attached on the firewall.

The #2 terminal on the side of the alternator comes up from the starter post. It has full battery voltage.

The #1 terminal on the side of the alternator runs through the firewall and disappears into a maze of wires. With the key OFF, this appears to be grounded. With the key on, it shows battery voltage.
unhook #2 see what happens, sounds like the alt can't turn off to me, the wire #1 heading into the cab should be for the idiot lite or gauge, that's why you see voltage on it with the key on.
a good starter and alternator shop can take your old 1 and convert it into a 1 wire alt, so then you'd just have the big heavy wire to the back and that's it, might be your best/quickest option, take the other alt back and get yo $$$$ back.
 

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Discussion Starter #5
unhook #2 see what happens, sounds like the alt can't turn off to me, the wire #1 heading into the cab should be for the idiot lite or gauge, that's why you see voltage on it with the key on.
a good starter and alternator shop can take your old 1 and convert it into a 1 wire alt, so then you'd just have the big heavy wire to the back and that's it, might be your best/quickest option, take the other alt back and get yo $$$$ back.
Hmmmm, you might be on to sumthin. I plugged in a spare plug and jumpered out #1 completely eliminating #2 from the system. MONEY!!!!

Between 14.1 and 14.2 volts on my voltmeter and in the truck.

Now, what is the purpose of #2 if it works so well without it???

Thanks so much guys. It's great to have some extra brains working on this with us......john

ps... we didnt buy an alternator. These are just spares I have in the shop. Thanks again
 

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Thanks Glenn.

With the mail wire that attaches to the lug on the back of tha alternator disconnected, I have full battery voltage to that wire terminal. That is the wire that returns from where the fuseable link attached on the firewall.

The #2 terminal on the side of the alternator comes up from the starter post. It has full battery voltage.

The #1 terminal on the side of the alternator runs through the firewall and disappears into a maze of wires. With the key OFF, this appears to be grounded. With the key on, it shows battery voltage.
This is what you should see...Like IMPATIENT says, the little wire is the the Uhmm Uh HMMM IDIOT light LOL...

You actually should see some resistance from it and not a direct "short to ground" but a reading over ground...

Is it possible that the large wire from the solenoid is broken and intermittent? This is the wire the alternator gets the charge condition signal from, it also sounds like maybe you have a potential for a fire, keep a set of diagonals and a fire extinguisher close by (the diagonals are to cut the wire if needed. The alternator is capable of a lot more than 30 amps BTW, that should be at least a 50 amp deal...:)bulb

Also may want to check for a bad body ground...Or I guess an engine ground...It would be odd that two alternators do the same thing.

When you read the disconnected alternator voltage, did you see AC or DC volts?
Also, factory radio? Some stereo shops do weird stuff :)grn
 

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Hmmmm, you might be on to sumthin. I plugged in a spare plug and jumpered out #1 completely eliminating #2 from the system. MONEY!!!!

Between 14.1 and 14.2 volts on my voltmeter and in the truck.

Now, what is the purpose of #2 if it works so well without it???

Thanks so much guys. It's great to have some extra brains working on this with us......john

ps... we didnt buy an alternator. These are just spares I have in the shop. Thanks again
wire #2 is the "exciter" wire...Sounds like you may have put in a "Single wire" alt...
 

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mo balls than $cents$
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Hmmmm, you might be on to sumthin. I plugged in a spare plug and jumpered out #1 completely eliminating #2 from the system. MONEY!!!!

Between 14.1 and 14.2 volts on my voltmeter and in the truck.

Now, what is the purpose of #2 if it works so well without it???

Thanks so much guys. It's great to have some extra brains working on this with us......john

ps... we didnt buy an alternator. These are just spares I have in the shop. Thanks again
let it run a bit and look again, i bet that 14.2 goes down quik, then again it may be charging, i've seen alot of dual hook up alt lately, the last 1 wire i bought for a boat could be hooked up either way and it'd charge.
 

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Discussion Starter #9
Wow this is wacky. It was working great with no drama and a steady 14.2 with #1 and #2 unplugged (making it work like a 1 wire). It ran that way for probably 15 minutes then took off on the charge voltage. I saw it and shut it down (and blew the fuse again).

Plugged it in exactly like stock using the #1 and #2 wires and it's now been perfect.

I traced the wires back to the solonoid and didnt see anything. I wiggled and pulled till I'm about crazy (there's a sig line for you) and it's working like it has for 3 years.

Something is still amiss but it's gonna take some thinking for sure...
 

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voltage regulator is junkkkkk, take it to a alt shop and have it converted to 1 wire
 

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let it run a bit and look again, i bet that 14.2 goes down quik, then again it may be charging, i've seen alot of dual hook up alt lately, the last 1 wire i bought for a boat could be hooked up either way and it'd charge.

I believe the only difference on the "one wire regulator" is it is internally connected at terminal #2 and "out"...

So both ways would make perfect sense...I just will not "reference" system voltage, but rather "battery voltage"..

Does that sentence even work? LOL
 

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I believe the only difference on the "one wire regulator" is it is internally connected at terminal #2 and "out"...

So both ways would make perfect sense...I just will not "reference" system voltage, but rather "battery voltage"..

Does that sentence even work? LOL
i understood it:D lol the alt i had that would go either way had a regulator in it that was made to do that, i think i saw that same regulator on ebay for sale the other day for about 20bucks, not bad.most alt shops around here charge about 35bucks labor and parts to just go in and install the 1 wire regulator, i think it was around 45 for the dual hook up type installed. either way the easiest thing to do is just have the alt converted to 1 wire, be done with the headache. if you do the ole jumper way, the alt will be on all the time with the key on, which will overcharge too, the regulator has to be able to turn off as well as on.
 

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i understood it:D lol the alt i had that would go either way had a regulator in it that was made to do that, i think i saw that same regulator on ebay for sale the other day for about 20bucks, not bad.most alt shops around here charge about 35bucks labor and parts to just go in and install the 1 wire regulator, i think it was around 45 for the dual hook up type installed. either way the easiest thing to do is just have the alt converted to 1 wire, be done with the headache. if you do the ole jumper way, the alt will be on all the time with the key on, which will overcharge too, the regulator has to be able to turn off as well as on.
I don't think so...Not 100% certain, but the way GM wired their stuff was to but the battery voltage directly to the #2 plug connector...Up until computers that is...(different alternator all together)..

Once the alternator stops spinning, the field collapses and it has to start all over again...you can literally run a short piece of wire from the post to #2 and be on your way, providing the regulator is not shorted that is...

John, I think you will find you have a short somewhere, a big one...And it will be on a big red wire coming from the alternator, or somewhere close....Remember the fire extinguisher...I want to see Ian get some EFI stuff for the Sanger...:)devil
 

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may be right, but he's still gotta bad regulator and it needs to be changed, better off just goin 1 wire now:)bulb
 

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Discussion Starter #15
Thanks again for all the help guys. Unfortunately it's now behaving perfectly like it has for the last 3 years. Did this alternator fix it, was one of the connections loose that I tighten up, maybe a wire was rubbing against something and all my Mickey Mouse'n in there clearanced it....who knows.

Now I need to have it do it again so we can tell. As it is now, it's all a go. Go figure....

And of course like any short box 4x4 chev of that vintage, a half dozen people at the very least have dinked around under the dash and it'd take me a month of sorting to figure it all out.

Thanks again and no Glenn, he's not getting FI before I do......;)
 

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I'd suspect you need to replace your positive (2-6 gauge) cable from the battery to the alt. (probably 2 cables one to the starter then from the starter)

What is probably happening is that, as the car warms the resistance in the already corroded or broken wires inside the insulation becomes a load and sucks the voltage from the system causing the alt to overproduce because its not seeing the numbers it wants.

it is completely normal to remove the pos cable on the alt. and see 30 or so volts on that empty lug you just removed the fat cable from. it is trying to output as much as possible because it doesn't think its outputting anything at all.

its clearly doing the same thing except after its gotten hot the thick pos cable resistance goes up, and the voltage read by the alt goes down so it ups the output more and more like it should. you get 30v output at the alt but 10v or so at the battery. as rpm goes up you start hitting the overvoltage limits of the radio and when you shut it off it spikes back and pops the fuse.

the easiest way to see if this is your problem is get it fired up again and wait for it to start outputing a large amount of voltage at the alt lug. once it is above 16-17v move the neg lead from your multimeter off the neg terminal of the battery (when you were measuring output from the lug on the alt.) and put it on the pos. terminal of the battery. with the pos. lead of the multimeter still on the pos. lug of the alt. you are now measuring voltage drop over the pos thick cable from the alt to the battery. (vehicle must remain running when you do this) if you see more than about a 1-1.5v when the alt. lug is outputing 16-18v its too high. if you wait till the lug shows 30v on the alt you should expect to see 15-18v on the multimeter when you have the pos lead on the alt. pos. lug and the neg. lead on the pos. post of the battery. if you see this value i can assure you the poss. cable or a connection of the poss. cable from the battery to the alt. is bad and needs to be replaced.

this is very easy to check without changing or really doing much work at all. i could be wrong about this, but i've seen it many times and it acts very similar to what you are talking about. try the tests as i said, and if it doesn't make sense i will explain it better. hope this helps

Andrew
 

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John I sure hope you didnt let ringer work on Ian's truck again........;)

Good to see you two got it figured out bud!
 

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Discussion Starter #18
I'd suspect you need to replace your positive (2-6 gauge) cable from the battery to the alt. (probably 2 cables one to the starter then from the starter)

Andrew
Thanks Andrew. I think we'll just replace all that wire and be done with it for good. It's a nice old truck and deserves some TLC. So far it continues to be behaving but I suspect it'll come back.

John I sure hope you didnt let ringer work on Ian's truck again........;)

Good to see you two got it figured out bud!
Hah! Don't be stirring up trouble Travis. Take care..
 

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John, how is the body grounded to the engine/chassis/battery ? Use a 'jumper cable' to quickly connect a test ground from body to battery negative post. All of the GM 'old style three wire alternators' will charge at near full output when rev'd up over 1500 RPMs when only the one large output wire is connected. Great if you like 'boiled battery with acid sauce'. The #1 wire is the 'load' wire. It is the one that turns on the regulator and is the one connected to the "idiot light" on older cars. It should have a load, like a light bulb connected to it, so the motor will shut off when the key is moved to off. The #2 is the power lead for the field. It can be connected dirctly to the large post on the back of the alt. Speaking of the large post and it's wire. That 10 gauge wire SHOULD go back to the starter solenoid, and be directly attached to the large battery cable post there. Quick and easy way to 'convert' these alts. to "one wire" is to replace the '3 wire regulator' with a 'diesel pickup regulator', they are one wire. Check all the grounds....
 

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Discussion Starter #20
Will do George. I want to go over all the connections but unfortunately ran out of time today.

So, how you been? Been building any cool stuff lately? Take care of yourself
 
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