I have a '77 C-10 with what looks like an over-charging situation. Before I started throwing parts at it, I thought I'd check here. Then I could throw parts smarter ;)

It has the standard 63 amp alternator (Pep Boys reman, about 5 yr old <8k miles on it) that was showing about 13-14 volts charging. I thought that was a bit high for all the time, and suspected the gauge that was of questionable parentage anyway. I installed a NOS volt gauge, but then it was showing in the red zone (~17 volts?) when running at hiway speeds. Okay, the battery was about 7 yr old, a bit iffy in cold mornings, so maybe it was using too much voltage to keep it going. New battery installed, same problem.

I brought the alt to Pep Boys under the lifetime warranty, but their machine showed it running betwen 14-16 volts at the very modest test speeds they use to spin them. My issue is it will do that for me, too at slower speeds but the hiway revs (>2500 or so) is when the much higher voltage reading occurs.

I am suspicious of a bad internal regulator, but have also run the distance on my electrical knowledge :rolleyes: . I know it's certainly possible to have a bad new volt gauge. I am inclined to get a reman alt from one of the ebay rebuilders with 135 amp capacity since the 63 amp seems a bit miserly (normal for the day, I know). BUT: any thoughts or tests anyone can suggest would help. The truck is bone stock BTW, so no heavy current draw equipment on it.

Thanks much!

Brian

Take it back to pep boys, and ask them to test it on your truck.... and rev it up to freeway speeds. There test equipment will tell you if it is good, and your guage is junk.... or the otherway around.

BTW, 13 - 14 is about right.

I was hoping not to have to do that, since I would prefer an easier diagnosis than bringing it over and probably having to leave it with them. But I may end up doing just that.

Thanks.

Put a multimeter on the batt terminals while its running, have someone rev it up to the higher RPMs and see what the reading is. If its 14 volts +/- .5volts your good to go. The gauge just might be bad.

Mike

Thanks, I will try that when I get a buddy to rev the engine. No one here but me right now.

I did a variation of that test at idle this afternoon when I reinstalled the alternator. May have gotten my answer, since the multimeter showed ~13 volts, but the volt gauge was well less than that.

stock guages weren't very acurate back in the day...ad a couple dozen years, and 1/4 million miles (or what ever it has) and they are that much worse.

My 77 chevy does the same thing. Bought checker rebuilds and after 2 or 3 years they do the same thing. All but one tested good. The one that was bad was shooting out flames on the tester, guess I was lucky as I drove it from Beumont,TX to Lubbock, TX after my wedding with every electrical switch on including the headlights and the needle was only on the edge of the red. My son drives it now and rather than replace the last one, we run the blower on high when at highway speeds. Keeps the needle out of the red! Man, i sound cheap. Guess I better go buy a new one for it. I think it is the internal voltage regulator. Maybe I should buy new instead of rebuilt, looks like I may just keep the pickup.

Joey's Toy, thanks for that info. I still haven't had time to check the voltage across the battery at higher revs, but I also don't feel so crazy now :crazy:

Somehow it doesn't surprise me they only test them under the most benign, low stress condiitons and then pronounce them "normal".

What's bothered me, too, is the volts gage is a NOS unit. While it may be inacurate even new (could have been dropped through the years, or just aged and became faulty), two days ago I got readings that varied +/- a volt or two at the same speeds at different times. And the same load drains you mentioned (lights/blower) made it read lower output. I'm not an electrical pro, but when I see variations like that I get real suspicious of that internal regulator, too ;)

Fortunately, a reman unit is <$40, so it isn't like a huge expense.

I ended up getting a 135amp alternator from Alterstart in the Dallas Tx area. Got it on ebay, and he has very good feedback. Holds 14 volts like nobody's business, unflinching. Cost ~$90 with shipping but seems to be a really good unit with a lifetime warranty.

Had 3 reman 100-amp alternators from local Carquest in 4 months and 2 were low voltage and 1 was over voltage. All were lifetime warranty. Ended up just getting my money back and ordered an Alterstart 135 amp alternator. Was cheaper than local store and also has a lifetime warranty. Also just got last month was their mini race starter with a lifetime warranty.

Glad to know I am not the only one happy with the Alterstart units. Thanks for that feedback. If I need a starter, I'll probably call them.

I am (slowly) learning Swervin' Ervin's addage "you get what you pay for" :metal: