2006 250xs - Alternator

[yellowjacket5]

Okay, the electrical gremlins are at work. Here is the situation. It appears that there is a resistance issue with my motor that is causing the alternator to fail. I have gone through three alternators in the course of just a few months. After about five hours on the new alternator, it begins to fail. The alternator is capable of maintaining a charge of 14.2v while running at a low to mid-range rpm; however, as the rpms increase the voltage begins to drop until it gets to the point (11.4v) that the guardian system takes over. Now, if I drop the rpms the voltage jumps right back up to 14.2. The alternators have been taken apart and sure enough they look like they have been put through the wringing. It is like clockwork, a new alternator works (no voltage problems) for about 5 hours until it has become worn to the point where it cannot maintain the voltage at high rpm (above 4500).

So, what has been done regarding looking for the resistance? Every imaginable thing that is easy to check has been checked. We have been on the phone with Mercury and have done everything that they have suggested with no luck. Is there something that is not obvious (i.e., the common places that one would look) that we should be looking?

Any novel thoughts would be greatly appreciated.

Thanks

[EuropeanAM]

Remove the GROUND CABLE for the alternator COMPLETELY.

Check it, and it's connections VERY carefully. Clean all connections points, and reattach it (tighten connections properly).

Also recommend checking the NEGATIVE battery cable attaching point AT THE CYLINDER BLOCK (below the starter). Clean the connection, clean the bolt's threads, and reinstall.

Verify integrity of the alternator output lead (clean end connections, ensure that the cable has continuity through it). This cable has a fusable link in it (the fuse link should be just about adjacent to the PCM).

Don't forget to LOAD TEST your battery- clean the connections, and reattach them ENGINE CABLE FIRST, then remaining ones "largest to smallest". Finish off the connection with a stainless locknut.

You've got a connection problem SOMEWHERE.....