What makes you so sure it is the relay? Anyways, just swap the defrost relay next to starter relay. It is same part number. If no joy, you don't have a relay problem. You will need to go further into this. Maybe a starter cut relay, or ecm wiring issue, or P/N or clutch safety depending what trans you have. Here is wiring.
Ok, it an auto. So start by checking the main fuses first.
The starter relay is not in the underhood junction box. It is located beneath dash left hand side in the instrument panel junction box. Can't miss it. Like I said, you can swap the defrost relay which is located right next to the starter relay if you doubt that relay, but I think you need to go further in this.
Your reply of yesterday says much more than a car that won't start. You say it died WHILE driving which has NOTHING to do with a starter relay or starter circuit. I would focus on main power sources and various sensors first such as crank and cam and check for B+ at EFI relay.
A big help for you would be to hook up a scanner to it and see if the scanner powers up first and shoots a code or two.
The EFI relay is in the underhood relay/fuse box, if you can hear it clicking when key is put to the ON position, that is a good sign.
If you don't have a scanner, you can at least check at the DLC connector for power there. If no power there, you will have a no communication problem with the ECU.
So, I will repeat my self, if the car stalled while driving, it has nothing to do with the starter or it's relay . If you say the battery is good, how did you check that? Have you at least jump started the car. Maybe the alternator gave out, battery got so low you stalled out. Who knows at this point,
Be patient with me, I will be patient with you. Answer my questions as best you can. Tell me your level of capabilities with a multi-meter and diagnostics skills, I will adjust my level to yours and help you find satisfaction. I am a toyota fan. I know these cars by heart. A guru of sorts.
It is not unseen for the EFI relay to quit on toyotas, so I would definitely start there. Make sure you have adequate starting power at battery. Make sure all main fuses are ok.
On these models, you need to think of the EFI relay much as like a mopar car that uses a Auto Shutdown relay. This relay supplies B+ to the ECM/ECU. In order for that to happen both the main fuse and the EFI fuse can't be open. Open meaning blown.
A relay like this is on all the time once the key is turned to the on position, right up until you shut the car down. So that relay can get alot of usage as you can imagine. A starter relay will only get abuse when cranking the key. Once the key is released, the starter relay and it's circuit are no longer of use for normal functions of the car.
Although I can see why you are fixated on a starter problem, you said it quit while driving, so something way more important than just the starter relay or starter gave out here. Even if you could bypass the starter itself, which is hard to do due to it's location, you would still just be only able to crank the car, and I bet my cats life ( I hate it so no big loss there) that the car still won't start.
Ignition switch gets power to crank from a black wire. When key is turned to crank position, the red wire should have power. If power goes into switch through black wire, but doesn't come out at red wire when key is turned to crank position, the problem would be a bad switch.