How to install new SI batteries...

[Jedz123]

So like many I have failed to find a walk through to install new SI batteries on this forum so I thought I would make one.

Some of you like me were plagued with a dead right sided instrument cluster and unlike a stroke victim we can resurrect those slumping extremities we call gauges with a little do-it your self project!

First we need supplies here's what you need:
Fully charged NiMH Rechargable AA batteries.

The innards of a AA battery Pack (mine is from Radio Shack)

Tools; that include Chanel lock, Philip and Flat head screwdrivers, soldering gun and solder, electrical and duct tape(preferably Gorilla glue kind), A knife and some patience.

First remove the Instrument cluster... I won't walk through how to do that, It's not to hard.

Once the cluster is out of the car bring it inside to work on it on a counter top or table.

First remove the backing of the instrument cluster by removing 8 Philip head screws. The gauge clusters should slide out and it should look like this.


The SI board is snugged in by two thing now, A plastic piece and that's screwed in on the inside of the gauge cover(Light Duct for CHECK Light) and a micro chip clipped on the front.

Remove these two things and slid out the SI board.

Now comes the fun, inspect the SI to see if there is any damages to the board from possible battery leakage. Unfortunately mine was in pretty rough shape. If yours looks bad just get a new board. Here is what my board looked like when I pulled it out. As you can see the Batteries are soaked in electrolyte and corrosion has set in all over the board.


First step is to remove the batteries. The Batteries are held in by pressed divots. I used a very small flat head screw driver to release the old batteries. Be careful not to break off the terminals! I used the channel locks to press the terminal back to a flat position. And make sure to clean up what mess you can from the old batteries!

Remember what side is Positive and Negative! The batteries are labeled!

Now install with solder the new AA battery terminals(Make sure to cut the springs for the batteries wont fit at normal Length) I covered the ends with tape to make sure that nothing would contact the terminals.

Now Install you batteries!

I put extra duct tape over the batteries to ensure they stayed in place

Then reinstall! your done!

My results were better then expected for I thought the whole SI board was done for. But to my amazement my Temp gauge flickered back to life! My Tach and Econo. gauge will randomly convulse then quit randomly. I'm guessing that the SI board was exposed to to much corrosive electrolyte for far to long. I'd replace the SI board but I'm getting a new tach anyway so I don't see a purpose anymore.

So hope that helps Good luck!
-Jedz

[yammahamma]

good write up....have you thought about mounting the batteries outside the cluster? That way when you have to replace (or recharge) them, you don't have to pull the cluster out.

Also...my SI batteries weren't marked + or -, so to save myself headache I just replaced the board.

[Jedz123]

NO never thought about that, To late to make the batteries external now...
My SI board is shot the LEDs never worked on it... I guess the battery change was almost a lost cause at least I got one gauge back! I'm getting a new Tach anyway for my performance ECU comes in next week... Dont' see any reason to get a new SI board.

[MercBimerman]

Nice write up. I remember doing this to one of my E30s many years ago. But I purchase a AA battery case from RadioShack with long wire leads.
I soldered the leads into the board (after removing old batteries) then ran them outside the cluster and mounted it behind the knee bolster.
That way if the batteries ever failed in the future they would be easily replaced without having to take the cluster out again.

[mikemellowz]

When you are replacing SI Board , then also remove instrument cluster
If you can not reset your Service light then you have to change the SI BOARD batteries.
These batteries are intended to save the service indicator memory in case you disconnect the car's main battery. When the car is running it recharges the SI board batteries. But over time they lose their ability to hold a charge and that is when the SI system starts to go haywire.Ones i had faced this problem and i am not been able to fix it.Then i had taken my car into BMW Repair Dallas and they fixed it.