I am currently designing a part that should always be on when the key is turned to On/Acc, and only sometimes on when the key is set to Off, or removed. My car is a 99 Camry, but I have a good understanding that this should be the same in any car.
The question I have, is the only difference between a car 12v always on circuit, and a switched 12v circuit, a physical switch (the key)? If I place a jump/short between a 12v always on wire and a 12v switched wire, is there any real difference?
The wiring Diagram makes the key switch look like a simple physical switch, while the 12v lines, both Always On, and Switched, look like they are electronically the same?
Update: This is the general idea I am working with. The Relay will self latch when SW1 is press, or when the car is on ON/ACC. When the relay latches from the 12v On\ACC, the diode should go into reverse bias so the circuit would then be powered from my fused Always On circuit, not the On\ACC circuit, while preventing backfeeding from Always On to the Switched circuit. I know a second relay would make things easier, but part count is important.
So, I guess the real question at this point is simply, not counting the fuses (just for theory), the Switched 12v and Always On 12v are the same exact lines, but the switched 12v has a physical key switch in the say, right? Shorting the two is bad practice, but nothing that will have major problems right?