I have an '89 E300. The battery is recent and tests good. The alternator is getting +2vdc on the D+ terminal and has +13vdc on the B+. The dash battery light comes on when the engine is not running and shuts off when it is running. All per spec.

The problem is the voltage on the battery when the car is running is 12 to 13 vdc. Which means the battery is not charging. I've removed every fuse with no change in symptoms.

I took the car to a shop where they told me I needed a new alternator. I bought an aftermarket rebuilt and installed it, got identical symptoms (though I've not been back to the shop to retest the alternator). When I first installed the new alternator, it sounded different and the voltage was +14vdc, but that lasted less than a minute and since then it has always read battery voltage.

In reading other posts, I saw where people used a test light to start the alternator by putting +12vdc on the B+ terminal. This did not work for me.

I'm considering delicate adjustments with a hammer. Any better suggestions?