Help Needed with Simple Relay Circuit SOLVED

Situation: My septic tank currently has one red warning light that turns on when the tank is full. When the waste water level is high enough it triggers a float switch. The red lights tells me it's time to empty the tank.

As things stand now, what happens if the bulb goes bad or I've lost electricity to the warning light circuit? The situation is ripe for an unexpected overflow.

Plan: I'd like to build a better warning indicator. I recently purchased two LED lights, one red and one green. Both lights will be mounted in a weatherproof outdoor electrical box. I'll drill two holes in the box cover plate, one for each light. Here is my light bulb logic. A lit green LED light indicates there is power to the circuit. When the float switch is triggered, the green light turns off and the red light turns on and it's time to have the tank emptied. Should I ever find both lights off, I'll know the situation needs to be looked at.

I've attached a crude drawing of what I think the circuit might look like. I know I need a relay in this application but I'm not sure what kind to get. Both LED lights operate on 120v. So I'm guessing I'll need a 120v relay.

Questions: Is my circuit accurate? And what type of relay do I need and can you point me to where I can purchase it. OK, that's three questions.

Keep in mind I'm not an electrical engineer. But as a homeowner of 25 years I've done plenty of basic to intermediate electrical work on my home. Last year I trenched and ran power to my detached garage and installed a new 60 AMP lug. All this was needed to power a new 240v table saw.

Thank you,


by JohnH76
July 10, 2017

3 Answers

Answer by JohnH76

Thanks for the feedback. This is an outdoor application where weather, animals and other factors could cause a component to fail. Without the relay, if the red light or the wiring between it and the relay fails, the light won't come on and I won't know my septic tank is full.

With this in mind, I think I've got it correct now.


ACCEPTED +1 vote
by JohnH76
August 24, 2017

Yes, that looks correct now.

by jzdeath
August 24, 2017

Thank you!

by JohnH76
August 25, 2017

Answer by jzdeath

The relay setup is incorrect but is not needed anyway. I would suggest removing the relay. Just connect the greed LED to the power side of the switch. Then the green LED will always be on. If the green LED is off you know power is off.

+1 vote
by jzdeath
July 17, 2017

Answer by mikerogerswsm

Yes - wot jzd said - you just need to replace the relay coil with one wire and its contacts with another wire and your schematic is correct!

+1 vote
by mikerogerswsm
August 04, 2017

ps - could do it in duplicate for added safety!

by mikerogerswsm
August 04, 2017

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