OK, Brain trust, help me out here, I'm questioning myself.
My problem: I am puttingheated/cooled seats in my truck, and it's a homebrew project. Each seat has two modules. Each module has a fan and a heating element. For cooled seats, the fan has to be on. For heated sats the heater AND the fan have to be on. I've already wired the seats, and have them run to plugs. Each seat plug has three pairs of wires. Cooling fan, heater 1, heater 2. Each heater is about 8 amps, and the fan draw is miniscule. I'm running the power to a set of relays (per seat). One relay for cool, one relay for hot. (relay's are rated at 40 amps). I have a blue button, and a red button. I want it wired so that when I push the blue button, the cool relay closes, and whe I press the red button BOTH relays close.
My solution: Wire blue button to cooling relay. Wire red putton to heating relay then jump from trigger pin of heat relay to trigger pin of cool relay with a diode "pointing" towards the cool relay. That way when the heat relay is triggered it will also close the cool relay, but when the cool relay is triggered the diode will keep voltage from "backfeeding" and closeing the heat relay.
Right? This should work? Diodes (that I can get at radio shack) can handle indefinite use at the amperage that closes relays?