using relays for auto on solutions

Sorry guys, with the holidays I haven't been around much to answer lately, but I appreciate the responses. I just started to read them over today. To answer some of your questions though: It is a 2002 Jeep Liberty. I'm not sure what you mean by verifying the wires, but I know which wires and which at the moment. The inverter has an on/off switch, so I would like to keep that switch set in the on position at all times so that I can just leave it and forget it. The inverter is just there to power the laptop, but when I'm about to turn the jeep off I put it into hibernate, so it can't last a bit even if there is no power from the inverter while the vehicle is off. I don't care if I have the ability to turn the inverter on/off while driving, just want to make sure that it turns on when I turn the ignition, and that there is no power draw when the engine is off. In regards to the hard drive, it is tucked under the rear passenger seat, and requires 12v which comes from from Carnetix. There is also a USB B which runs to the external usb hub (5v, also powered by carnetix) then USB to the laptop. There is a toggle switch for either on/off. I would also like to make it so when the ignition is turned on, hard drive turns on, when ignition is off, hard drive powers down. I'm sorry for the lack of details earlier, I should have been a bit more clear. Also, I thought IGN/ACC were the same thing, that's why I had mentioned it before.

It is still the same solution. One relay supplies +12V to the lot. ACC is off during cranking/starting whereas IGN remains on.

Or better still, run the relay off the charge light circuit. (Like a fuel pump or aux battery relay.) But if you want it to stay on after an engine stall, it should control a latching relay (circuit) with a separate button to turn it off.

Can you throw me a link to what I'm looking for specifically, as far as a relay goes? Because I've found this: http://www.google.com/products?q=TRIAC as well as this: http://www.google.com/products?hl=en&client=firefox-a&rls=org.mozilla:en-US:official&hs=Azm&q=automotive+relay&um=1&ie=UTF-8&ei=up8SS4P5MtWYlAfO4IiMBA&sa=X&oi=product_result_group&ct=image&resnum=4&ved=0CC4QzAMwAw so I'm not really sure what I am looking for.

See adding a second battery (page-3; 2nd reply) for info on an 80A latching relay. Not that is what I had in mind.... The on-whilst-charging method I use is to connect a relay (solenoid) from the alternator's charge lamp circuit (commonly labeled D+ or L) to ground. The relay the energises when the alternator is charging. It's a common method of powering (electric!) Fuel Pump relays (so that fuel pumps turns off if the engine stalls). However not all charging systems will handle the relay. If you already have a similar relay (like an existing relay to power the fuel pump or other loads), then no problem - you trigger your new relay from that relay's switched output (rather than adding another solenoid to the charge lamp circuit). Otherwise you could add some buffer to remove your power relay's solenoid load (typically 60 Ohm or about 200mA) so as to not load the charge lamp circuit (maybe an intermediate high impedance relay with 160 Ohm, 400 Ohm, or higher), or a transistor circuit etc). Or you could control your relay from another circuit - typically the air-flap for EFI vehicles, or thru an ignition detection circuit which is ON whilst there is still spark (either method often being used as a backup for fuel pump relays). Or there is the Oatley K227 "Dual Battery" kit that is also linked from the above "adding a second battery" to here. The Oatley kit K227 (AUD$22.00) can duplicate the charge lamp circuit functionality wise - ie, its relay is ON when the vehicle is charging. Although it switches 80A, in your case I'd just use it as the "charging signal" for your power relay.    A disable switch is easily added, but the push-button "off" switch would still have to be pressed to open your relay (and kill power to your system). Standby for a diagram of the latching relay system..... (PM me if I forget.....) I wouldn't worry about triacs or SCRs. Besides, they can be tricky to turn off in DC applications.

How's this as a systems diagram? (schematic etc) It may have errors, and it isn't quite a wiring diagram though enough info should be presented for the semi-experienced. And it has its own ramble.... PE: FIXED!!! If the filename is too long, images won't post & you get just the red square! #*^%&*!#!! Guess who uses descriptive filenames!