The Stovebolt Site Forums The Shop Area The Electrical Bay Generator Light on - 59 GMC 1/2 ton w V8

I have a "new" (rebuilt) generator and a new regulator and the red gen light is on. Goes off when idling, but comes on about half-strength when driving. New belt has 3/8" of deflection. I took it to my mechanic and he said that I needed a new regulator so I got one. That didn't fix the problem. This started just after I had the engine pulled to replace an undersized piston (long story). Any ideas? - Michael

Michael,

I know very little about generator & voltage regulator diagnosis.

Did you polarize the generator?
(a brief touch of "jumper" lead between Armature & Battery leads on the voltage regulator will do it)

You have to check the generator output for 13-14 Volts. Bulb has 12V on both ends, if gen puts out 12V+ light stays off...or if 12V+ is not getting to one end of bulb, bulb lights up. You may want to check bulb input wiring. Be sure to check your battery at rest, should be 12.6V. You need a voltmeter.

Check to be sure there is a good ground between the engine and the frame and/or the battery negative terminal. Also check for a ground wire between the generator housing and the regulator base- - - -install one if it's not there now. If there's a slightly high resistance anywhere between the generator and the battery, the charging current will try to go through the idiot light and cause it to glow. Check for clean, tight connections at the back of the ammeter, and the end of the wire from the ammeter where it attaches to the battery cable at the starter.
Jerry

I understand you saying ever thing was ok with the gen and reg until you replaced the engine, and then you started having problems.. roger that? and even with the problem your battery is still staying charged. I would think that with an engine switch you would have not messed with much wiring but..

I have a voltmeter and the battery is over 12 volts. I did "jumper" the voltage regulator when I installed it (per the instructions). There are three wire lug connections on the generator. How do I check it? Which one is the "hot" one?

Get rid of the generator and the voltage regulator. Put in an alternator. There are a whole bunch of grounding issues, adjustment to gaps on reg., old wiring, old generator brushes, winding problems and etc., which are much less of an issue with an alt. Search in here how to swap, it's not hard.
If not,
READ THIS:
http://www.netlink.net/mp/volks/htm/gen.htm
This guy says 35V output, my 55-59 GMC manual says stock Delco Remy gen is 14V output at 2780 RPM. and 25 amps.
Gen part no. 1100304 (V8) or 1100336 (6cyl). There were optional generators available. If you want that info, give gen part no.
Those "Tell Tale" bulbs do come on at low RPM and go off as you drive.(increase RPM) That is normal. Should go OFF at high idle and above.

Here are some steps to take.
1. Check battery water and general battery condition to
see if it will take and hold a charge....Load testing
may be necessary.
2. Check wiring for damage and make sure all
connections at generator, regulator and battery are
tight and free of corrosion.
3. Make sure fan belt is tight enough to drive
generator at full capacity.
4. Run engine at medium speed. Using a wire, touch one
end to regulator base and other end to a good ground.
If this corrects trouble, regulator is not properly
grounded anymore.
5. If test 4 does not correct trouble, make this test.
Connect a wire from regulator terminal marked "ARM" or
"GEN" to regulator terminal marked "BAT" with engine
running at medium speed. If charging rate increases,
replace old regulator.
6. If test 5 does not correct trouble, make this test.
Connect a wire from "FLD" Terminal of regulator to a
good ground with engine running at medium speed. If
Charging rate increases, replace old regulator.

If none of the above test show a bad regulator then
there is probably a problem in the generator itself.

Good info Kenneth, Can you tell him and me how to check "if charging rate increases"... with a tell tale bulb system? Is it that if the bulb, which is staying on at higher RMS now, goes off? Don't know if there is an amp gauge or if it works.

Attempting to check out a charging system without an accurate voltmeter and ammeter is a total waste of time. The ammeter on the dash is just a rough guesstimate of what's going on, and an idiot light is even worse. If the battery is staying charged and the light is on, but dim, there is a high resistance connection somewhere. You're going to need to find someone with enough electrical knowledge to be able to measure the voltage drop at every connection between the generator and the battery, which eliminates virtually all automotive hobbyists, and at least 90% of the so-called professionals in the auto repair trade.
Jerry

Like I said, switch to an alternator. No more regulator, much less interconnects/terminations/contacts/old stuff.
Get into the solid state world baby. Transistor sister....And it does not take an expert or much equipment to trouble shoot an alt. and they are cheap. I say this advice for TF folks, especially V8. AD's, not so much.
Do you have the old GMC/Pontiac 347 V8? 336?

Like Jerry said, without the correct tools your shooting in the dark. If you have a meter check your current battery voltage...write it down. Turn on headlights etc. and drain some juice out of the battery. Take another reading at the battery and write down the voltage. When you crank the truck your going to draw your battery down even more. With your meter hooked up watch your voltage and you should see an increase. Increase your rpms and watch it.....you should see an increase in the voltage. If not your probably not getting charge into the battery.

The original charging system is pretty straight forward. Your generator has an armature, field coils and brushes. You have a external regulator that controls the generators output. Any charging system...alternator or generator must have proper grounds and connections. Thats basic stuff. There is nothing wrong with the original system if its built correctly....CORRECTLY being the key word. Any rebuilder is going to do just that....rebuild, with good used parts. I NEVER use a used armature in my restorations..its a waste of time, you can test them on a growler etc. and they may test good...even test good on the test stand, but as soon as you install it, the unit goes south. I always use NOS or rewound armatures to my specs. With that being said I would be curious as to what your rebuilt generator consisted of internally. I would take it off, find a local rebuilder and have it tested alone after I checked the ground, especially to the regulator.

An alternator isnt always a cure all. A standard 10SI, which is the most popular Delco alternator used on these conversions, has a rotor, or armature if you will, stator, diode trio, rectifier bridge with a set of pos. diodes on one side and neg. diodes on the other, an internal voltage regulator and a brush rack. They are very good alternators "if built correctly" and typically last a long time. However, any of the above mentioned alternator parts can fail at any given time. You MUST have a good ground and good connections on an alternator as well.

Alternators are cheaper, no doubt about that as the cost to install new parts in a generator these days is expensive. This all becomes a personal preference and ultimately is up to you. Let us know what you find.
Regards,
Ken

Just to give poster info, not to be argumentative: A 61 Amp alternator is $50 and has a lifetime warrantee. As in; you never have to worry about cost again. You can't beat that with a wooden stick. If you are stuck on keeping it stock appearing then that's a factor, as mentioned. I don't believe in torture though.