First of I'm a newbie on this forum, so I really don't want to step on any toes, I kind of plan to pick your brains on EV's as much as possible... Buuut... Since I'm kind of good with designing circuits, I kind of think I can add something... And the circuit here has a little design flaw... Not something that makes it not work in normal operation though...
Mora... A few questions on the design... The diode D1, what is it supposed to do really? Cuz right now it's not really doing anything a normal wire couldn't do...
My guess the intention is to protect the circuit? Ie swap ground and +12V and nothing goes poof?
Then it really should be connected to the ground wire... Facing so that the ground flows out of the circuit is open, but nothing goes in that way, since that is what makes things go poof... Connecting ground to +12V won't make anything go poof... It just won't do anything hooked up that way, no lights, no magic smoke...
Another thing to remember when doing protection... In this instance it's kind of an moot point as the protection doesn't really do anything as it is anyway, but right now R1 is connected to the "outside" leg of the diode... Ie even if the diode in theory would protect something the R1 would still give a path to destroying stuff when connecting things up the wrong way...
And unfortunately two wrong does not make one right...
Move the diode to the ground connector and have it block the path into the circuit and it gives protection... As it sits now you can just replace it with a wire and the circuit will work the same...