I do a whole bunch of Avalons; there's a better way.
What model Avalon? XL or XLE? With or without a factory alarm system? Generally, only the ones with all the options have the alarm.
If you have the factory alarm, you'll want to go into the driver's door. It's only three wires you need to interface with, and removing Toyota door panels isn't that hard. But this will be a challenge for a novice.
Here's the easier way, at least for me:
The factory lock relays are built into the fusebox somewhere. It's not possible to activate them directly, at least without dissecting the fuse box.
On the right side of the fuse box, are the doorlock "motor" wires. Blue/red is to lock all the doors, blue/white unlocks the driver's door, and blue unlocks the other three doors.
Right on this website you're on now, off to the left, click on Door Locks, and then on "5-wire reversing polarity" for a good diagram of what you have to do. Here's a direct link: https://www.the12volt.com/doorlocks/page3.asp#5w
That diagram shows two relays; you'll need to wire a third in a similar fashion, since your car has two-stage unlocking.
The only hard part of this is understanding that diagram, and wiring accordingly. You just find those three motor wires, buy three relays, and "five-wire" all of them; simple.
If you pop out the panel holding the dashboard dimmer and far driver's side air vent, there's enough room to put your relays in there.
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| ITEM | WIRE COLOR |POL| WIRE LOCATION |
| 12V|wh/blu(40A)wh/rd(10A|+ |ignition harness |
| STARTER|BLACK/ white |+ |ignition harness |
| IGNITION|BLACK/ orange |+ |ignition harness |
| SECOND IGNITION|WHITE/ red |+ |ignition harness |
| ACCESSORY|WHITE/ green |+ |ignition harness |
| POWER LOCK|*1 | | |
| POWER UNLOCK|*1 | | |
| LOCK MOTOR|blue/red | |right side of the fusebox |
| UNLOCK MOTOR|blue/white | |right side of the fusebox |
| DISARM DEFEAT|blue | |right side of the fusebox |
| PARKING LIGHTS +|use (-) wire only | | |
| PARKING LIGHTS -|pink | |steering column |
| HEADLIGHTS|RED / yel, blk/yel *2 |- |steering column |
| DOOR TRIGGER|RED / blue or red |- |right side of the fusebox |
| DOME SUPERVISION|GREEN/ red |- | |
| TRUNK/HATCH PIN|red |- |left side of the fusebox |
| HOOD PIN|black |- |theft ECU *3 |
|TRNK/HTCH RELEASE|blue |- |switch on dash *7 |
| FCTRY ALARM ARM|arms w/ lock | | |
|FCTRY ALRM DISARM|disarms w/ unlock | | |
| DISARM NO UNLOCK|RED / yellow *5 |- |steering column |
| TACHOMETER|black | |drivers kick panel *4 |
| SPEED SENSE|PURPLE / white | |drivers kick panel *4 |
| BRAKE WIRE|RED / blue or grn/wht |+ |brake switch or pass kick |
| HORN TRIGGER|GREEN/ black |- |steering column |
| WIPERS|blu/blk(L),blu/org(H|+ |steering column |
| LF WINDOW UP/DN|green - red |A |LF window motor |
| RF WINDOW UP/DN|green - red |A |RF window motor |
| LR WINDOW UP/DN|green - red |A |LR window switch |
| RR WINDOW UP/DN|green - red |A |RR window switch |
| SUN RF OPN/CLOSE|not recommended | | |
| RADIO 12V|blue / YELLOW |+ |radio |
| RADIO GROUND|brown |- |radio |
| RADIO SWITCH|gray |+ |radio |
| RADIO ILLUMINATE|green |+ |radio |
| POWER ANTENNA| | | |
| LF SPEAKER|pink - purple | |radio or amplifier *6 |
| RF SPEAKER|lt green - blue | |radio or amplifier *6 |
| LR SPEAKER|black - yellow | |radio or amplifier *6 |
| RR SPEAKER|red - white | |radio or amplifier *6 |
Notes:
NOTE: Some models have an immobilizer system that needs to be bypassed during remote start. Use DEI module 555F or 555U to bypass. *1 For the door lock interface, see directfax document #1070. *2 Use RED / yellow on models with DRL (daytime running lights) and BLACK / YELLOW on models without DRL. *3 The theft module is located above the glovebox. *4 Located in a gray plug, with the wires going up to the instrument cluster. *5 This is the ignition key sense wire. Using the status output wire from the remote start to ground this wire will disarm the alarm without unlocking the doors. *6 The amplifier is under the front passenger seat. *7 Only works if main switch in the glove box is on.