What is the smallest size activating wire (small wire) that should be used to activate a solenoid that relays power to a starter on an 18 HP Briggs & Stratton twin cylinder? Is #16 too small?

#16 should work just fine to power the relay, as long as the length is not excessive. I can't imagine that you would need a very long length of wire to reach the solenoid.

Overall distance would be 4 to 5 feet. It will be used on a small train powered by the 18HP Briggs. Thanks for response.

A #16 copper wire can safely be used up to about 10 amps of current. I can assure you the relay isn't pulling anywhere near that.

fyi...The resistance of a 5 foot piece of #16 is about 0.02 ohms. This means that even if you were pulling the full 10 amps through the wire, the voltage drop would be a mere 0.2 volts!

Bottom line...you're good to go with the #16! :thumbsup: