Sitting in the drive thru line at, I noticed that my battery and brake light would flicker, and rpms wound randomly drop. No big deal, I've seen this before, so it must be the alternator. Had it replaced. During this time, and with the car sitting, the battery dies. So, I have it charged, and I slapped it in. Good to go right? Not so much.

Driving down the road on the new alternator, the battery and brake light fickers again. I pull over, throw the hazards on, and notice that the rpms are dropping when the hazards flash, and the interior lights dim with them as well. I checked to make sure that the battery terminals are tight and the lead wire to the alternator is snug. All good there. Might I mention, the car never died, and doesn't have an issue starting.

I took a multimeter to the alternator, and it read between 13.8 to 14.5 at idle with no load. Something as simple as rolling up the windows or the fans coming on would make it drop below 13 to 12.7, and it's VERY noticeable with the rpms and dimming lights.

Took it to the battery, 12.2v when the car is off, and about 12.5 when the car is running.

Please help me.... I'm really about done with this car, as it's the most problematic vehicle I've ever owned. Which is a shame because I absolutely love this car...

06M35

Since a power window can drag it down, there are really only three possibilities. The alternator is either losing regulation under load, isn't putting out its full rated current, or there's resistance in the wiring between the alternator and battery. First, check the fuse for the field winding. If it's blown, the alternator will still have output but very weak. The fuse is usually in the Fuse & Relay Box and not the IPDM, generally marked "ALT" on the cover diagram. You can check for resistance very easily with voltage drop. Turn on the high beams so there's a load and put one voltmeter probe on the alternator output stud, the other on the plus battery post. There should be no more than about 200mV (0.2V) of loss, and under 100mV is more like it. If the reading is high, you can step backwards through the terminals and cable just like using voltage drop to trace a bad ground. If that all checks out, inspect the terminals of the 3- or 4-pin connector at the alternator. It's very common for the connector shells to crack from heat and allow the pins to gradually corrode. If you don't find anything there, then it's likely the parts store simply sold you a bum alternator.

VStar650CL wrote: ↑

Mon Nov 08, 2021 7:45 pm

Since a power window can drag it down, there are really only three possibilities. The alternator is either losing regulation under load, isn't putting out its full rated current, or there's resistance in the wiring between the alternator and battery. First, check the fuse for the field winding. If it's blown, the alternator will still have output but very weak. The fuse is usually in the Fuse & Relay Box and not the IPDM, generally marked "ALT" on the cover diagram. You can check for resistance very easily with voltage drop. Turn on the high beams so there's a load and put one voltmeter probe on the alternator output stud, the other on the plus battery post. There should be no more than about 200mV (0.2V) of loss, and under 100mV is more like it. If the reading is high, you can step backwards through the terminals and cable just like using voltage drop to trace a bad ground. If that all checks out, inspect the terminals of the 3- or 4-pin connector at the alternator. It's very common for the connector shells to crack from heat and allow the pins to gradually corrode. If you don't find anything there, then it's likely the parts store simply sold you a bum alternator.

You know what, it's funny you mention the connector at the alternator. I did notice that it was very brittle, and began to Crack in my hand. The connection there is snug, or so it was at last check...

like most are 12.5+ Vdc off and above 13.x Vdc running , ya

Max2M35 wrote: ↑

Mon Nov 08, 2021 8:28 pm

You know what, it's funny you mention the connector at the alternator. I did notice that it was very brittle, and began to Crack in my hand. The connection there is snug, or so it was at last check...

It's very common. That's why there are replacement pigtails all over eBay and Amazon.

I had a similar issue and it was the terminals on my battery had just gotten to the point they were not tight and secure anymore after being used 15 years. I replaced my battery connections and the issue went away. Your issue may not specifically be your battery connections, but it definitely sounds exactly like an intermittent resistance issue in your wiring somewhere in your main electrical system.