I searched but had no luck. Sorry if this kind of thing has been answered a bunch. I'm designing a circuit for my car. If you wanna know more just ask and I will explain. I want to know when I need to use diodes to protect stuff. I have attached a wiring diagram. I know I need diodes D1 and D2 because those relays are being switched by a computer. Latching and Latching2 are single coil latching relays with a coil rating of 25mA 12VDC. Do I need D3 and D4? Those relays are activated by a physical switch with a rating of 5 amps but will only have 150mA going through. K1 and K2's coils are rated at 150mA 12VDC. Do I need another diode between the contacts of relay K2? Because of the starter solenoid? And now on to sizing. I have no idea where to start. I read Schottky diodes are what I want because of the whole .2V thing instead of .7V. I started to look on digikey, but realized I was in over my head. I pretty much just learned about diodes and relays within the last few days, so there is still much to learn. If you could give me some rules to follow (if there are any) when selecting diodes in case my specs change, that'd be great. These are the specs I know. Latching/Latching2 = Coil - 25mA 12VDC. Contact 10A 250VAC (won't see more than 150mA 12VDC) K1/K2 = Coil - 150mA 12VDC. Contact - 70A 12VDC (won't see more than 40A) Thanks in advance.