1998 Silverado, 350. When electrical load is placed on system the dashboard charging indicator shows charging drop. The more load, the more it drops. It recovers but everything that is in use momentarily loses power, not completely but enough to notice. I had the electrical system tested at an auto parts store for what that is worth. Tested ok. I'm thinking alternator but want some other opinions. Thanks for the help.

 

I would look at the grounding straps, and other electrical connections under the hood. A bad path to ground or degraded electrical connection can reduce the current you can pull, and cause voltage drops under load. I'm not sure what the auto parts store is testing, but if it's alternator and battery, that won't tell you anything beyond those two components, unless it includes a load test of some sort.

If all the wiring looks good, and the voltage drops under load, it is certainly possible that the voltage regulator, which is built into modern alternators, is going bad. When I was a teenager, I had a car that blew the voltage regulator almost yearly, and I would start noticing that the headlights would brighten and dim based on engine RPM. The voltage regulator used to be a separate component under the hood, but some idiot back in the mid to late 70's decided to integrate it into the alternator, requiring you to replace the alternator in order to replace the voltage regulator...

My 1996 C1500 had a bad starter, which the auto parts store people tested as good recently. I insisted on going ahead and getting a new one anyway, and carried it back to the house, and my truck was cranking again 20-30 minutes later. So I don't have a lot of faith in the abilities of folks working behind those counters these days.

 

Thanks, I'll check those connections. I've noticed a pattern to the problem that's interesting . The charging drop occurs every 17 to 18 seconds regardless of the load. Seems odd to me, ever heard of anything like that? The young lady at the parts store just connected some small electronic tester to the battery and waited for the machine to give a result, took about 30 seconds. I think unless the part was totally fried the test was not very complex.

 

Does it happen at driving speeds, idle or both?

 

Both.

 

That's weird that it's 17-18 second intervals, whether driving or parked. Doesn't sound like it's anything mechanical in other words. More like some load trying to switch on electronically, through a relay or something.

I think what I would do is this.

Fire things up, hook up a volt meter to the battery or however you can easily watch this voltage fluctuation, then start pulling fuses one at a time and look for a change. Start with the fuse box by the driver door. Then go to the fuse box under the hood. Just don't pull ones that will shut the engine down obviously. This might help you find what circuit is causing the drain.

 

I'll try it, thanks

 

Tried pulling fuses but no change. Didn't pull the ones I wasn't sure were needed to keep the engine running. About when the voltage drop occurs, it happens at low rpms such as idling and slow driving but not noticeable at highway speeds/1500-2000rpms. I ordered an alternator, hate to throw parts but going to try a new one, if the issue continues I'll have one thing crossed off the list.

 

If the drop doesn't occur at higher RPM, good chance it is alternator related. Let us know how it works out.

 

Installed a reman alternator from Carquest, no more voltage drops. Looks like it was the alternator, thanks for the help and advice.