# What is the purpose of the relay in this circuit?

I have tinkered with relays while building small projects with microcontrollers in the past. Usually I use them to switch higher amperage circuits off or on. I recently purchased this horn and this wiring kit for it, along with a small 12v battery. I also had to purchase an automotive relay that was not included in the wiring kit. However, I have no idea what the purpose of the relay is, since the horn is activated using the push button supplied with the kit. Could I have just wired the + terminal from the compressor straight to the battery, then wired the - terminal to the switch, then to the - terminal of the battery?

• What's the current draw of the compressor and the current rating of the switch? – The Photon Apr 20 at 17:45
• Usually I use them to switch higher amperage circuits off or on. ... why are you asking when you already know the answer – jsotola Apr 20 at 22:35
• "20A fuse" is a clue here. If you are using a 20A (or higher) rated switch, you don't need the relay. – Brian Drummond Apr 21 at 9:53