WARNING!-Bosch Rebuilt Alternators!!

[3D914]

I've been fighting the last week trying to resolve a alternator light that wouldn't go out - even after installing a rebuilt alternator, new regulator, changing the alternator light to 2W, and checking/cleaning all connections.

The source of the problem was only found after trying three Bosch AL75X Rebuilt Alternators. Based on BAP Auto, this is the Bosch replacement alternator for the 914/2.0.

The problem is with the design of the black cover that fits on the rear of the alternator to cool it, and the recent rebuilt alternators. This back cover does not come with the rebuilt, and must be removed from the core alternator and installed on the rebuilt - hence the problem.

The three-wire connector that caries DF, D+, & D- to the relay board is in one bundle, and the B+ wire that goes to the starter solenoid is a single separate wire. The AL75X has two studs coming out of the back of the alternator. One stud is taller than the other to permit connection of the B+ red wire.



Both studs on the AL75X have a large washer with an index tab, than a small washer, then the nut. The smaller stud (opposite the post for the B+ wire) is positioned such that the large washer will short against the cover when is is screwed down with the three small nuts.

This is the source of the problem, and will not be apparent unless you check continuity between the red (B+) wire and the alternator case as you assemble the cover. The flat on the inside of the cover will hit the edge of the large washer.



The solution is to 1) remove the large washer, or 2) snip part of the washer off - opposite the indexing tab.



Then when the washer is installed and the cover is in position, it will not short against the washer.



It is also suggested that once you have the cover assembled that you use your volt-meter to check for continuity between the red (B+) wire and the silver body of the alternator. There should be none.

Hope this helps someone else in the future.

Enjoy!

[woodman]

Interesting problem. I'll check mine out before I reinstall. Just picked one up.

Any idea which way to orient the back plate? Looks like it can go one of three ways.

[3D914]

Woodman,

Yes it can. The trick is to locate the flange where the alternator pivot bolt goes (the lower one when installed). With the alternator shaft toward you, the air-duct entry (on the cover) should point to the left and slightly down. This positions it to fit on the rubber vent boot that extends from the fan housing.

Good luck.

[Jim Smolka]

Great post. Thanks for the tip. We use Bosch alternators a bunch.

[jamcleod]

you da man! great tip, thanks for sharing

[greenwood]

I can only imagine the frustration you must have had trying to find this. Excellent job!

This needs to be put in the tech articles so it doesn't get lost under thousands of future posts.

[D7N7MASTER]

That would have pizzed me off.
I especially appreciated the pics along with the detailed description of the problem. I second that...excellent post. Thanx!!!