My alternator is not alternating

[Kevin_H.]

Oh wise and great contributors of the forestry forum, I am calling for your help.

My alternator on my 84 gmc c-60 is not alternating, er I mean charging, tonite I was driving home in the dark with no headlights, cause the battery was so low that if ya tried to light up the road the motor would die. Any way here I was easing my way across the rail road tracks when all of a sudden the darn thing started charging and I could turn the lights on.

Now we have had this problem in the past but I thought we had it whipped, On the back of the alternator we have the big red wire that comes off the lug, and we have a two wires that are in a clip that snaps into the back of the alternator, the two wires in the clip are white and green, the white wire hooks directly into the above mentioned red wire and the green wire runs behind the motor somewhere, (I did not want to lay on the cold ground tonite just to find out where it goes.)

The last time we had this problem a mechanic hooked a jumper from the green wire to the + side of the battery he said this would " turn " the alternator on, but to be sure to remove it while not running the truck or the battery would go dead.

Now I am guessing a short in the green wire might be the problem, but I thought I would throw it out to the masses to see what ya'll thought.

[Tom]

The first thing I would look for would be a loose or dirty battery cable.

It's got to be a loose or bad connection. 

Electricity doesn't usually slowly wear out.  :D

That green wire is probaby a tickler and may operate by the charge light which acts as a resister.   If the light burns out, the battery will never call for the alternator.  You can put a resistor in the line in its place if you can find out the size required.     It might be that the bad connection is the light itself.

[Gary_C]

It could be the brushes in the alternator. It is simple to rebuild those alternators if you get a kit with the brushes and a new regulator. The trick is to put a wire (paper clip will work) thru a hole right in the back of the case to hold the brushes back when you assemble. There is even a hole in the brush holders for the wire. Just mark the case halves so you get it together the same way and don't forget to pull the wire after you assemble.

Those old Delco alternators can also be found in parts stores or your local farm and fleet store as rebuilts and they are not too expensive. Do not worry too much about finding the exact listing. There were only about two case sizes and then the only differences were how the case halves were oriented when assembling. Originally there were different amp ratings but now all are rebuilt to the same amp capacity. You jist have to use your old belt pulley.

[rebocardo]

> Any way here I was easing my way across the rail road tracks when all of a sudden the
> darn thing started charging and I could turn the lights on.

That says bad connection. I would hazard a guess your alternator lead (that green wire) goes and gets its' (+) power from the (+) lug on the starter solenoid which is on the starter, which goes directly to the battery (+).

What your "mechanic"   : did by jumping that wire was just asking for a fire since that green wire (if it goes to the starter) is on a 12 gauge fusible link.

Three things most likely could be wrong:

1) one the splice is bad between the wire and fusible link, they corrode or break due to vibration and heat

2) the female connector on the starter itself is bad or corroded

3) It not attached tight enough (the nut has backed off). Happens after a starter is changed and the old nut reused.

[Coon]

The problem may also lie within the alternator.  Those Chev alternators have built in regulator that may be bad.  Check mall of your other wiring first to eliminate those possibilities.  If all wires are good and making a good clean connection then chances are that the regulator is pooched.  If you need a new regulator it comes with the alternator rebuild kit which is not very expensive.  If you don't want the hassle to rebuild the old alternator then you can purchase a rebuilt one fairly for a reasonable price.  The last one that I bought was around $45 Cdn. with the old one taken in for core.

[Modat22]

I had one on my s10 that did that, I got mad at it finally and bought one of those 1 wire alternators from JC whitney and just ran a new wire.

It was cheaper than a new alternator in my case, I had to have the pulley from the old alternator put on the new one though.

[Quartlow]

The 3 wires on a GM alternator are

1 Big one on the back goes direct to the starter, hooks on to the battery cable there, almost always has a fusible link in line. This wire is Hot all the time!!!

The two wires in the plug on the side, bigger one is the Exciter wire, comes on hot with the ignition. It CAN be wire hot all the time it WILL NOT drain the battery, My dozer, countless tractors and trucks at my brothers are all wired hot all the time

The smaller of the two wires is for the idiot light, not required. Idiot light gets positive juice from the ignition switch, ground comes from the alternator, If the alternator is charging ground is switched of by the voltage regulator and the light goes out. I have seen GM alternators that quit charging enough, And the idiot light never came on.

Get a voltage guage, forget about amp gauges they don't tell you enough. An alternator should show 12.8 to 13.2 volts with every electrical accessory turned on. anything under 12.5 volts your starting to drain the battery. I've had systems that showed 25 amps of charge rate  but only 12 volts, sooner or later it catchs up and the battery goes dead.  No load voltage should be between 13.4 to 13.8 volts, anything above that your overcharging which will result in shorter battery life

[submarinesailor]

Past experience for me, it was the brushes.  With the motor running, we would lightly tap on the alternator with a wooden hammer handle and it would start charging again.  I think it reseated the brushes against the rotor - for a few turns anyways.  Reseated the brushes and all was find.  BTW – it was a 65 Chevy truck.

Bruce

[Kirk_Allen]

Kevin I think your post title needs modified.  "My alternator IS alternating" 

It goes from on to off so I guess that would alternating  ;D

I am with Tom.  I bet you have a bad connection.  I would have a hard time believing its the alternator or regulator because when they go bad, they dont just start working again, at least from my experience. 

[Slabs]

Kevin

Maybe this diagram will help to understand what goes on in your charging system.  This schematic is from the shop manual in my old 74 K-10 and should be identical to your 80 modle.






Do you have an ammeter or Idiot light?  As you can see, the idiot light provides the initail excitation to start the alternator working or the resistor in the case of an ammeter.  Also, the large red wire from the stud on the back of the alternator may go th the ammeter(if used) or to the starter solenoid in the event of an idiot light.  The "extrnal starting excitation" is used until the rotor initially gets "tickled" and then the "triode" pack (DIODE TRIO)provides the current necessary to power the field coil/rotor.  (note: if the idiot light is own dimly during what should be normal operation, one of the diodes in the triode pack may be open and the assembly will need replacing)

The wire from terminal 2 is for voltage sensing and woould normally be connected someplace near the battery for an accurate reading but will work well connected to the power output stud on the back of the alternator.

AS you can see, GM shows the "tickler" lead from terminal 1 going thru the ignition switch.  I haven't checked the possible drain current that would be experienced if it were left "hot" all the time but from previous posts it must not be much.  Also the alternator will not begin to charge if the idiot light or resister is blown or there is a break in the circuit between the ignition switch and the alternator.

Many of the new alternators only have one additional wire going from the alternator (WM mills) that is the tickler and usually goes to an idiot light or in the case of WM the "idiot led".  Obviously the sensing is done internally in those cases.

On those older alternators there's a shorting tab on the brush holder that can be shorted momentarily to bypass the voltage regulator to determine if the regulator is defective but that trick is best left to someone who's done it before.

Hope this gives you and others some help on operating and servicing.

Good luck

[Kevin_H.]

I knew the forestry forum would come through, The alternator is new, we replaced it when all this first started happening, we have not had the time  to crawl under it yet but talking to the mech. at work they seem to think that the green wire or tickler goes back to an idiot light on the dash, although I have never seen one while turning the key on, it does have a volt meter and it seems to be working alright, They think that it might also be the resistor in that green line.

Anyway all things are pointing to some kind of short in that green wire, or where that green wire terminates.

On the jumper that I put back on, we are not leaving it hooked all the time, If we notice that the battery is getting low and we havn't hit enough bumps  ;D to make the alternator start then I touch the jumper to the + side of the battery just long enough to start the alt, and then remove it.

Thanks again for the imput, hopefully we will have time to dig into it next week, when we find the problem we will give an update.

[Coon]

I talked to a guy yesterday and he was telling me about the same kind of problem he was having.  He then went on to tell me how he got it fixed and what exactly was the problem. ;)  He couldn't get the DanG thing to charge properly and went he told his bro in law what was going on he said that it was definately a regulator prob.  Jack told him no it could not be that cuz it was a new alternator.  Henry said that yep it is and that he could prove it. So on Henry goes home and comes back about 10 min later.  He went home to get his test light and his brand new spare alterator.  He used the test light and something was not working just right in there.  Ah ha yup the regulator was weak and was cutting out when it got hot.  They switched out the alternators and the new alternator was charging and everthing was back to normal.  Henry basicaly told him that they would go and take the alternator back to the place where he got it.  There they told him exactly what was going on and exchanged the alternator and were content again.