how can I wire up power inverter to secondary battery, but turn on when car starts?

I have a 400 watt power inverter that I am going to use for my carputer. It is going to be hooked up to the secondary battery I have in my spare tire well. Problem is, if the car is turned off, the power inverter would still be on. I hate to have to turn the power inverter on and off every time I get in and out of the car. Can I use a relay from the ignition wire, or from the remote turn-on wire of my head unit, so that the power inverter will receive power only when the car is on or head unit is on? I already have a relay hooked up to the remote turn-on lead off my head unit to my 4 amplifiers, so could I simply run an extra wire off that to a relay for the inverter. Any suggestions?

Tap into the On/Off switch of the inverter by soldering a wire to each contact (take the inverter apart and access the back of the switch, it's usually a rocker type switch). Then use either your remote turn-on or another ignition-on wire to power a relay that would basically flick the switch on and off for you.

yeah, go to radioshack and buy a .5amp 12vdc reed relay. Hook up the +12v REM wire to one side of the coil, and ground the other side to your ground in the trunk. Hook up the switch on the relay to the SPST switch on your inverter. Make sure the relay is normally open..... The inverter will turn on with your ignition.

Why do you have the extra battery? Your gonna have to use some type of switch at the front of the car if you want to be able to use the inverter with the ignition off.

Geez man, 4 amps? That's sweet. You can do like all Nick and dodge said. With that much stuff, have you considered buying a DCCS to power on all of your hardware?
That might make your install and power up go more smoothly

Just a suggestion

I have an extra batt in spare tire well because of my pretty big stereo setup. 2500 TRUE watts RMS. this is not BS watts that are advertised on the amplifiers. I've done the research, and the math and pulling a true 2500 watts RMS just for the stereo, not to mention over 30 neon tubes and accent lights and an underbody kit. the thing is pretty much a mobile club, lol. I so have a stinger relay which is connected between the two batteries and isolates them from each other when the car is off, but connects them as one loop when the car is on, so the alternator can charge them both. thanks again for the help