Diodes, Diodes, and more diodes

We talk all the time about putting diodes in line with the sensor lines to keep feedback and such from disrupting the normal flow of "info", however, for some reason I just thought of this last night: Why is it we do NOT put diodes in line with lets say - the parking light wire or the ignition wire, etc, etc...so that when we turn on the lights or we start the car with the key - we do not send that 12-volts surging into the brain? Am I just being paranoid or has the designers already thought of this and have put them in the circuit inside the brain?

because basically inside the brain is a relay that just puts out 12v, where as the inputs may provide feedback and arn't isolated when not in use like the outputs are.Just a Guy, Wiring up those Vehicals

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Gool_Greg

Well Im glad then I was just paranoid! :)