Good morning!

I have a 1989 740GL, NA, with 272K miles and have had an issue with the alternator not charging consistently. The dash lights started coming on at low speeds, especially while turning corners, but would generally not come on otherwise. Voltage at the battery with the engine running was about 12.7v - 12.9v and didn't increase when the engine was would rev above idle. After a few days of this, the dash lights would come on briefly even at highway speeds.

The things I have tried are:

1. Tightened loose alternator belt. No change.
2. Replaced the 5yo battery and the regulator/brush assembly on the original alternator. No change.
3. Replaced the alternator.

Now, the battery voltage with the engine stopped is ~12.7V. With the engine running at idle, voltage at the battery is 13.7v - 13.9v. With each accessory that's turned on (headlights, fan, radio) the voltage drops and settles around 12.4v at idle and may increase to 12.5v - 12.6 when revved.

One thing I noticed today is that the dash lights come on when the voltage drops to about 12.2v and this is happening in my driveway as I rev the engine. This voltage drop must be happening as I drive as the dash lights come on briefly then as well.

Can anyone point me in the right direction to properly diagnose and repair this problem? I don't know what to try or where to look next.

Thanks for any help.

Dh

--
1989 740GL (272K)