Quick mod to maintain engine battery from solar supply

Yes, but I would have to run a new wire from the house to the engine compartment to reach the engine side of the relay or the battery itself.

My next little project is to make a step down alarm that rings when I start the engine with the step down. I am thinking of a magnetic switch on the step that switches off when the step is up. I have an easy route for wires from the switch into the house and hopefully can get from there to an engine on live fuse in the inside fuse box.