Here is a rough sketch. When you press the normally open momentary switch on the right, the coil of the relay is energized. That applies 12V to the LED and to the coil so that the coil stays energized once you release the momentary switch. Wire the device you are controlling to the momentary switch as well. To open the relay press the normally closed momentary switch on the top. You can use two circuits like this with two DPDT momentary switches. Switch A energizes relay A and opens relay B and switch B does the opposite. It can be done with three switches and three relays (for three actuator positions), but it gets a little more complicated.


right beside the controller for my Espar coolant heater 