[shorod]

Of course it was parallel to the battery, in close proximity to the audio amplifier. Putting it in series would block the DC source to the amplifier.

The best way to see the noise in the electrical system would be to set the scope to AC coupling and take the DC component out of the equation. Then you could clearly see the noise and ripple component on the electrical system. Using a high gain amplifier could introduce switching noise depending on how well filtered the power supply is (noise figure). If you have a good amplifier that's installed properly, there should be sufficient isolation between the input power and the gain stage to not have experience ignition noise anyway.

I will also add that the ONLY time I've experienced a failed ECU in a car, it was due to a few 105 degree C electrolytic capacitors in the ECU that failed prematurely (in this case due to a chemistry issue).

-Rod