An "otto-start" circuit is employment of a relay , triggered by the ignition's switch "start" position, and providing current to the driver's-side spade terminal of the starter solenoid from (usually) the big "battery" post of the starter solenoid or any other high-powered junction (maybe an installed distribution block)... Thus, the trigger current of the starter does not pass through your valuable and expensive ignition switch (but through the cheap and easily replaceable relay), which removes load and prolongs it's life. You can find plenty of information on the subject if you do a search in the electrical section...