How do I wire in a light to turn on when the 2nd pump kicks on

 

Wire it in with the Hobbs switch or a second relay whatever you're using so when the second pump kicks on it sends power to the light as well. Pretty straight forward

 

What he said. Simplest way would be to hook it up to a good ground. For the hot (power) side, just splice it into the Hobbs switch or relay where power comes out only when the switch or relay is on, if not the light will just stay on.