Hey all. I know I've seen similar topics on this before about alternators on this particular model not charging, but I've seen nothing like what I'm experiencing.

I've got a 1976 240D 115 chassis, brand new Bosch alternator. I had intermittent connection issues with it before, and that was from the engine shaking lose the connection to the alternator, therefore making the "battery not charging" light FLICKER on and off. I fixed that. NOW however, my light comes on after I start it, but FADES as RPM in the engine increase. Sometimes, if RPMs hit a certain height, it'll "stick" and the light will stay off for a while, which means it's charging like it should. But, low and behold, it will turn back on and do the fade thing in relation to engine RPM again.

I've tested my battery, being a new battery, and it holds a good charge. I've measured the voltage after starting the engine, and when the light is OFF, which means charging, it's an expected ~14V. Whenever the light is on, it's at ~12.6V, which means not charging. I have no idea what's going on here, I've tried damn near everything. I've tightened the belt, it's never squealed once, when I look at the alternator, I can see it spinning fine.

The ONE thing that may be an issue that I'm just not understanding could affect anything: there is a small crack on the alternator bracket on the side where the teeth meet the star bolt tightening system thingy. It's not NEAR the teeth at all just on the same side, it's where the bracket is bolted and can pivot up and down off of the block. I personally didn't think this could cause what is going on, but hey, I'm here asking for help now. What do you think? Simple belt tension stuff due to the crack? Or electrical stuff being weird? Thanks in advance!!