truck not chargin

[cflvulcan]

one night driving home i lost all power. i checked it and the alternator wasnt charging. its been almost two weeks now. i went and bought a brand new alternator and voltage regulator and put in new wires and connectors but still not charging. any ideas????????

[71tahoe]

Was the battery dead too? I've had alternators quit and still limp a little ways on just the battery. There may be a bad ground somewhere or a fusible link blown.

[tshaw72low]

Im having same problems, Ive replaced everything as well..

Tommy

[84_4x4]

is the battery any good

[JimKshortstep4x4]

Did you check the exciter voltage coming from the ignition switch? It should be 12 volts or less since the feed wire is a resistor.

Jim

[ChevyC102007]

Im having the same problem, batterys good (still takes a charge) Altenator is new (about 3 months old) and so is the regulator. Havent checked the ignition wire yet but I am contemplating a conversion to a newer three wire GM altenator.

[72lb4x4]

Three people with the same problem, but none post their battery voltage with the engine running and not running. This suggests that in some cases the problem may not be what they think it is.

These are pretty much the first questions that should be asked.

With the engine off, a charged battery should have about 12.5V.
With the engine on, a charging battery should have about 14.5V.

[ChevyC102007]

Well lets see, when I checked it not to long ago it had 13 volts flat engine off. Started engine and the voltage on the battery dropped to 12.8, as I increased engine speed to around 1500 to 2000 rpm the battery volts went to 15, and as soon as I let off the throttle they began to drop....................now whats that and indication of? Rememer the PO cobbled up the wiring on the truck.

[jhow66]

Did you hook the ground wire back up at voltage regulator? Also there are two different regulators-one for light and one for gauge type.

[ChevyC102007]

All wires are hooked up to the regulator, also for whatever reason the PO unhooked the amp guage but I did buy the regulator for the guage type.

Didnt mean to hijack the gents thread, just wanted to put in my two cents since Im having the same problem.

[tshaw72low]

I replaced the voltage regulator and alternator, battery replaced and fully charged.. 12.5v with dead motor.. Traced all fused links and they all tested good.. 12 volts at key switch.. Replaced both battery cables and ends..
Traced all grounds and made sure they were all good, <cleaned and reseated contact points>


The wiring on inside of cab is all really nice, <No hack job been preformed by PO>

I put around 60 miles on truck today and checked battery as soon as I got home and it was at 60% charge..

:edit: The battery with motor running never gets over 12.8v
Tommy

[72lb4x4]

Chevy, that's an indication that its not charging at idle, but it is once the revs come up.

Tshaw, 12.5 off and 12.8 running? Not much improvement, but it suggests the alt is putting out something.

If its an external reg, it may need adjusted. Not sure how the calibration is from the parts store. Service manual...

A quick look at the wiring diagram suggests that you might check voltage at the big red alternator wire while running. Maybe to the engine ground, and to the battery ground.

http://67-72chevytrucks.com/vboard/s...d.php?t=185856

Are there ground straps from the engine to cab, and cab to frame?

[ChevyC102007]

Ok heres another dumb question. According to the book I have it says to use like a half ohm (I think thats what it is) probe in the Horn relay to help set the voltage going through everything (now what in blazes does the horn have to do with the damn charging system anyways ) but it dont show where it is...................where in the heck is it?

[67ChevyRedneck]

This may be helpful:

http://67-72chevytrucks.com/vboard/s...d.php?t=230011

I had the same problems y'all are having. I got tired of it after 3 voltage regulators, 2 new batteries, and a new alternator. I got fed up and converted to an internally regulated alternator and got rid of the external voltage regulator. You can read through my post and in the first post is the link to the FAQ on how to do it.

Keep checking for bad wiring and grounds first.

[72lb4x4]

What book would that be?
The horn relay is on the inside firewall to the left of the steering column.
I don't see how messing around near the relay will help, other than it has 12V on the red wire.

Since you are charging above idle and assuming you drive the truck, its probably spending most of its time charging.

Since the wiring is cobbed up, its hard to guess, but I'd charge the battery, drive it to the parts store and have it tested.

As stated very recently in another thread, charging a battery to ~12V doesn't mean it will hold a charge, or reliably start the truck.

[tshaw72low]

Update:

I was having trouble with not charging, ext voltage reg <was replaced 3 times>, Alt <new> and has new battery. I checked all grounds and replaced all that didn't look good to me..

After checking all the grounds and replacing the new battery again it's charging now. But now it charging a little to dang good. Peggin my gage out on the + side when rev'd up, Ive checked battery with motor off and have 12.7v and running charging goes up to 14.7 +v.. This is driving me crazy, I dont know what else to do..


Tommy

[Andy4639]

When the truck is running it should read 14. something, this is right for a running engine. (open road reading or with RPM'S reved up) If you turn your lights,radio,a/c heater and such on while the truck is idling this is where you need to have the battery checked. Everything on and truck sitting at idle. The reading should stay above 12.5, if not you have a bad regulator or one that wasn't set right. The externals were bad for not keeping the battery charged while everything was on. If you sit in traffic a lot then it want ever fully charge it either because of the low RPM'S.
Oh make sure the belt isn't slipping either.

OK now for what the 1971 manual say's
Running engine at 1500RPM'S for 15 minutes or until it's warmed up. Voltage should read between 13.5 to 15.2.
There is a screw inside the voltage regulator that can be set up or down. This set's the out put voltage for you.

[ChevyC102007]

Ok sorry been working my tail off lately so Im just now getting back to this thread. The book I have is a Haynes manual for 67-87 Chevy trucks (emphisus {sp} on 87 seems to have more to do with 81-87 Chevy's) Anyways, it as well as the Auto Zone online manual both state to check and set your voltage to use the half ohm tester in the horn relay .

I do drive the truck (just not to Cabelas during the week since right now it wont exactly pass a gas station although my wife drives it back and forth to work and around town while Im working) but it doesnt fail every month or so I will have to pull out the charger and extension cord and recharge the battery (Wal-Mart special). I dunno, between Cabelas during the week and working at the local gas station on the weekends and other things I aint got time anymore to work on the truck .

[72 longhorn BB]

Hi, I am involved in this mystery right now as well, and reading the MAD forum, I have learned a couple of things there, and just got another question to clarify on this thread.

1.) The horn terminal is also the busbar, or junction block connection point between the wire coming from the alt and the wire going to the batt.

from what I understand in the drawing on the MAD site, the reg has its sense wire (term 3) connected at this point too.

The charging system is designed to sense and maintain voltage at that horn junction block at whatever the reg is set at, hopefully factory set is around 14.5 volts.

Anyway, this article goes on to say that from the junction block, a red wire goes accross to the psgr side of the car to the battery, and that this wire drops the voltage along the way because of its size and length.

they say that it drops about 1 volt on way to battery which actually helps keep the battery from constantly being slammed by 14.5v. (batteries need less volts to maintain charge in hot weather, more volts in cold weather)

I also know that once a copper wire gets real old, the individual strands get verdigree (oxidation) on the surface of each strand which increases the resistance of the wire. Increased resistance = more voltage drop = less voltage at battery. this could explain why an otherwise healthy system is failing to keep a full charge on a battery.

I plan on changing the red wire from the alt to junction block on the horn relay and junction block to battery with a 12 or 10 ga new wire, to reduce the voltage drop.

Anyhow, when you diagnose the system, you have to set up a spread sheet and measure the following points at the following engine conditions.

key in run, engine off
engine cold (just started) at idle
engine warmed up (5 min) at idle



with this you can compare readings and see where the values drop.

I give credit to this image to the good guys at MAD website:


Now, whats all this about two different regulators, depending on which dash you have? I never heard of that before.

-

[ChevyC102007]

From what I know if ya just have the "idiot" lamp on your dash there is a regulator for that dunno why but thats what I know. I have both, "idiot lamp and the volt meter (which isnt either working and needs to be replaced or was just unhooked) so thats the one I have. Dont know exactly the difference in the two but maybe someone else can explain it better than me.

I am going to starting next spring build another 350 for Ole Blue and I will convert it then to the three wire alt but until then I just wanna be able to charge the battery while the trucks being driven, getting tired of the monthly charger routine. thanks for the advice I will try and check a few things today since I gotta replace the water pump in my wifes car

[oldgold70c10]

Idiot ligths or not, the regulator *should* be the same. All the ammeter in the gauge dash does is tell you which part of the system current is being drawn from. One lead of the ammeter goes to the battery + terminal, the other goes to the alternator + terminal. These will be light gauge black wires with inline fuses to protect the ammeter. Check your ammeter wiring and make sure it is working, it will tell you a lot more about what's going on than simply knowing the voltage.