I've done one RX300, but dozens upon dozens of Toyota Highlanders, which is the same car. The Techsoft information is basically accurate. I've found a few extra things.
Like all Toyotas, the climate controls run off the second ignition wire. The pink wire just does the radio and power mirrors and stuff----it's not needed for remote start.
Going to the brake pedal switch sucks----you can easily find brake, and positive parking lights, together in the driver's kick. There are two plugs there; the wires you want are in the plug toward the rear of the car.
Auto-headlamp shutoff: If your remote starter has any type of output that makes a pulse upon remote start shutdown, do this: Peel back the carpeting in the driver's kick; locate a taped-up harness with about five or six wires in it. RED / blue is the driver's doorpin; red is the two rear doors----tie your output into one of these wires-----it will simulate a door being opened, thus turning the headlamps off. These are low-current wires; a relay should not be needed.
On the one RX300 I did, I couldn't find any easy way to get a wire through the firewall for the hoodpin. If anyone finds a way, or finds the factory hoodpin wire inside the car, please add the information here.
The RX300 comes with a special, credit-card style spare key. This separates into two pieces----the key is a plain metal one, and the transponder chip is held in the plastic credit card. You can use the credit card thingy for remote start, but it of course won't fit into the 555U........
Get yourself one piece of very long, thin wire. Pass about half of it through the slot in the credit card, so you have lots of slack on each end-----now loop it around in such a way that you have made two wraps around the transponder, and tape the wire in place. You'll now have two long lengths of wire in your hands. Take one end, make it go straight for about one foot, and then wrap it twice around the car's key cylinder. Now, bring it back to where the other free end is........tie these two ends to terminals 87 and 30 of a relay, and set up 85 and 86 to be activated when the remote starter is on. You mustn't twist these wires with your drill, or loop them around other things----keep them straight.
HOW TO DO KEYLESS ENTRY:
It's a little tricky, but not hard once you understand how the system works. I forget the wire colors, but I'll give you an overview and you'll be able to find them yourself.
First, find and test these three wires---they should all be at the power window switch:
Lock wire---it tests by twisting the key in the door, NOT by using the rocker switch.
Unlock wire----again, it tests with the key in the door.
Unlock detection wire----often, but incorrectly, called the "child safety wire:" This wire will show a ground if the doors are unlocked; and be dead (or nearly dead) with the doors locked.
HOW TO UNLOCK:
This is the easy part. Take your unit's negative unlock output, split it with two diodes. One side goes to the unlock detection wire, and the other goes to the unlock wire. When the car sees both wires go negative at the same time, the door(s) and hatch will unlock.
NOTE: If you do this in the passenger door, all doors open on a single pulse. If you do it in the driver's door, only the driver's door unlocks on the first pulse; a second pulse unlocks all the others. Also, in either case, this disarms the factory alarm too. Furthermore, as long as the motor's not running, the factory domelight supervision kicks on too. NOTE: I use Audivox units with strong 300ma lock/unlock outputs.......if yours is weaker, you may need to use a relay to give enough strength to power up both of these wires at the same time.
HOW TO LOCK:
A little trickier here, but not too bad. Two things need to happen to lock the car-----the unlock detection wire must go dead, AND the lock wire must see a ground, at the same time. To do this, you'll tie your unit's lock wire into the car's lock wire, AND at the same time, to the 85 terminal of a relay.............
Cut the unlock detection wire in half. One side to 30 of your relay, the other side to 87a---doesn't matter which is which. 87 will be unused. For the constant power you need for the 85 terminal, there's a thick constant wire at the power window switch----no need to run your own wire from inside the car for this.
So, here's how it happens: When the user presses Lock on his remote, the lock wire in the car sees a ground, and the relay temporarily interrupts the unlock detection wire, fooling the car into thinking it has gone dead, and thus the doors lock. Also, this arms the factory alarm.