The correct procedure is to disconnect the ground (negative) terminal from the battery. This will make it safe for you to work on the electrics without inadvertently causing a short circuit which could immediately burn out your wiring (or worse).
This may sound strange to you. Why disconnect ground? Wouldn't it be more logical to disconnect the voltage carrying (positive) terminal from the battery? Well, there is a good reason. First: electrically speaking it does not matter which terminal you disconnect. When the circuit is broken no current can flow. It does not matter whether the circuit is open at the positive or at the negative terminal. BUT ... When you loosen the bolt or nut at the positive terminal of the battery you will need to use a spanner. When turning the (steel) spanner it may easily touch a metal part of the car body. That will create a massive short circuit! In fact you have now turned the battery and spanner into an arc-welding set-up with all the associated fireworks. I would strongly advise you not to try this. However when you first loosen the clamp on the ground terminal you can have the spanner touch the body of the car without any ill effect. The only thing to look out for is that it does not touch the positive terminal of the battery.
As for waiting 15 minutes, that's BS. It can be done in 2 minutes, just press the brake pedal multiple times to get rid of the residual current.
To really know if you have reset the ECU via this method, you'll see your guages go crazy when you put your key in and start her up.
Important thread though.
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