This is a guide of how to connect a Remote Start to the rear defogger on a '94 Camry. This is a bit difficult to do, because the timer for the defogger is built into the button. It requires modification of the button (you won't be able to tell its been modded when you get everything back together, except that the defogger timer will activate when you remote start your car). You'll need 22 Gauge or close enough wire, and a small relay (radioshack, nothing special needed) that has Normally Open capability.
You'll have to take the defogger button out of the car, and open its casing to expose the circuit board. The harness connector is for 6 conductors, but only 5 in use. Drill a small hole through the spot for the unused conductor (big enough to fit 2 wires easily, but not too big to damage the used conductors), and drill the same sized hole through the casing and the harness itself. Basically the 3 holes have to work together so you can feed the wires out from the circuit board, through the harness, and into the empty space behind HVAC controls to attach to the relay. I hope you understand what I mean. Now, while you're looking at the circuit board, you should see a smaller circuit board thats attached to it. There are two metal leads next to each other that connect the two boards, these two leads are shorted while the button is pressed in (i.e. to (de)activate the timer). You need to solder a separate wire to each lead, 2 wires, 1 each lead (the wires can be the same color). And run these wires through the hole you drilled. Once all the soldering is done, you can put your button back together. And connect it to the harness (it'll require extra effort to run the 2 wires through the harness, so take your time). Once its connected to the harness test it. (Make sure the two new wires aren't shorted or touching ground!) Turn the key to "On" and see if you can press to (de)activate the defogger like normal. Obviously the remote start won't do anything yet. But just to make sure you haven't messed up yet.
Now pre-wire your relay with short (3" or 6") wires. For the coil, if it is labled for positive and negative, use different colored wires so you know. And then you'll need two wires that will be Normally Open, and Closed with 12 volts to the coil. So 4 wires all together from the relay. Make sure you know (by color, or w/e) which wires are coil, and which are switched...obviously, sorry if I insulted anyone's intelligence.
Now to put the relay in between your new-fangled defogger button, and remote start! The Red-BlueStriped wire going to the defogger switch should be spliced to the positive side of the coil. The negative side of the coil should be connected to the Remote Start's (-) Defogger Activator wire. The two Normally Open wires should be connected to the two wires you added to your button. And the setting for the Defogger Activator should be "Pulsed" not "Latched." And thats it, test it with button presses, and with remote start to make sure it works. Then put everything back together.