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Submitted By: fixb52s
Date Created: 04-25-2006
Description: Some things don't work. All the gauges and various waning lights are dead. These things can be easier to fix than you might think.
Related Projects: 1989 BMW 325ic Restoration
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Old radio
The radio was dead. Now was a good time to replace it with a CD deck. The speakers were good, so they were reused, after the factory amp was removed. A lot of extra wires were spliced into the speaker wiring and had to be removed.

The extra wires were from a LoJack that was installed in the past, but was long gone. They were doing nothing, so all of the extra was removed.

New radio
The new radio deck looks like it was made for the dash. There will be no added amps and woofers yet. Boom boom will have to wait.

The tach and fuel gauge were dead. No surprize, because this is a common BMW problem, something learned with an old 528e. BMW put batteries in the dash clusters on an "SI" board to keep the service indicator lights working in the event the main battery went dead. The problem is these batteries go dead too, and they need to be replaced. When they go dead, the gauges die along with them. To replace them, the cluster must come out.

The cluster must be taken apart to get to the batteries. It is not as bad as it seems.

On the 3 series clusters, the SI board is separate from the main. On the 5 series, it is a part of the main cluster.
SI board location

SI board
This is the 3 series SI board.

These are the batteries that go bad. Ni-Cad batteries were used in some boards, and others use lithium. Ni-Cads have a problem with leaking when they go bad, eating the board in the process. A new board can be purchaced for $150 plus your old board. Batteries made in 1992 do not work well in 2007.
Old batteries

Out with the old
To replace the batteries, the board that holds the batteries must be removed from the main board. Desolder the posts as marked.

With care, the boards are seperated. The posts are heated up and a desolder suction tool was used to remove the old solder. Only heat the solder enough to melt it, and quickly clean it off.
Battery board removed

Batteries removed
The batteries were desoldered and seperated from the board. New replacements came from an online store since no electronic stores locally had them. They are Sanyo CR14250SE, and have the correct posts. Similar batteries can come from Radio Shack without the posts and can be soldered on the old posts once the batteries are seperated from them. This would eliminate one from seperating the boards.

Solder the new batteries on, then resolder the 2 boards, being careful not to bend or break the posts. Reassemble and install the cluster. The SI indicator was reset so the "service now" lights were off. There are tools to reset this, but procedures are online where a jumper wire is used with the service plug under the hood. The indicator is reset, and the gauges work again.
In with the new

Operational check
Turn the key, and it lights up. (The brake lining light comes on when the key is turned to start, and I did have the engine running prior to the photo, so the temp gauge is up).

Hey, the tachometer, temp gauge and mpg indicator work now. The fix for the speedometer was a pick up sensor located on the rear differential. Mission complete.
Working like it should

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