12 volt power to DPDT relay coil to magnet reed switch to ground. One NO contact; coil ground to NC push-button to ground. One NO contact; 12 v power to HD relay to ground. One NC 12 V power to LED to ground.
Using a magnet to close the reed switch energizes the DPDT relay, energizing the HD relay opening the circuit you want to control, it also switches the LED off. The circuit through the push button keeps the relay 'pulled in'. Push the button opens the circuit holding the relay allowing it to 'drop out' this lights the LED and allows the HD relay to de-energize and close the circuit you are controlling.