Instead of having the current flowing through the switch and that old crusty Purple wire to get to the starter solenoid; aka the long way around, your starter power now comes directly from the battery, and all the key does is to actuate the relay so the battery current can trigger the starter. if your wiring is that suspect, you might wish to add other relays to various circuits like the headlights and horn. They are not that hard to wire in and make your factory harness a whole lot happier because it no longer has to handle primary current flow.
Nick
Nick