The ECU box is located in the engine bay,on the right side, at the bottom of the windshield. You wil have to disassemble a part of the cabin filter cover to be able to access the ECU box cover. There are several allen head screws to remove.

I suggest you disconnect the negative terminal of your batterie first just to be safe and not shorting anything by accident.

Here is a link showing the install in a 3 serie. You can skip to 'Step 4' where they connect the trigger wire inside the ECU box.

On the picture, it shows a red/white with yellow stripes. I don't remember having yellow stripes on mine, but once in there, you will see those red/white wires are bigger than the rest of the signal wire.

Also, I suggest to skin and solder the wire connections instead of using crimp on devices. But, if done correctly (good size of crimp on for the corresponding wire gauge), there shouldn't be any problems.

FastM.com (2003.5 BMW M3) - DIY Guide for 60LED Angel Eye Kit

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