4-28-26 Hella mirror relay markup.jpg

My Rydeen Tombo 360 aftermarket backup camera draws something like 25mA with occasional spikes to 100mA while the car is off and it is in "power off" mode. I think this is from the g-force sensor and maybe the proximity sensor, both of which use constant 12V to trigger the 360 camera to record for 30 seconds when the car gets bumped or it detects someone nearby. While I love this feature when parked in public, there's really no need for it in my garage. And after a week without driving, the battery is noticeably drained and I feel like there is a difference in cold starting speed between 12.4V and 12.6V.

A simple cutoff switch would look out of place in the car, and I probably wouldn't remember it. But I have the 8-channel Wings-a-Loft kit and I'm only using 4 right now (Lock, Unlock, Driver Door popper, Passenger Door popper), and when you have a hammer everything looks like a nail.

I found a HELLA 933364027 "bistable relay". The relay has magnets in it and essentially only requires current when it is switching open or closed. Once in a position, the magnets keep it there with no current needed. So the plan is to wire it up so that I can control it with Channels 5 and 6 on the Wings-A-Loft key fob. This doesn't require any additional current other than a half-second of around 100mA to flip the relay on (when I lock the car in public) or off (when I get out of the car in my garage). There is a way to do this a bit more robustly with two additional standard auto relays, but space is at a premium in the relay compartment and this is a one-micro-relay solution that seems to get the job done in bench testing.

Essentially the Wings-a-Loft gives a one-second-duration ground connection when the key fob is pressed. That is enough to make the current from the 12V yellow wire pass through the resistor and pull current through the relay coil to that pin. Grounding the other wire does it for the other pin. So essentially by triggering the ground connection, it momentarily allows a rush of current to energize the relay coil and toggle it to the magnet on the other side. At least that's my understanding!