Engine will not crank all I hear is a click?

So I did not mention that at first when I installed the new starter, I sent power to the starter to make sure the engine will turn and to see if the starter is good. The starter engaged, rotating the engine. But when I pressed the start switch, it just clicked. I found that the starter relay was not sending power to the starter. Then I tested the starter relay by ohmning it and sending 12v. Relay was bad. I then bench tested the starter and it did on spin for a second but did not engaged. I sent the starter back for a replacement. While I'm waiting for the replacement, I connected my scan tool to see if the switch is engaging and the switch reads crank on the scan tool when pressing the start button. But here's the thing, on the starter relay it has 4 pins (1, 2, 3 and 5). Pin 3 is constant 12v. Pin 5 is the switch side going to the starter solenoid. Pins 1&2 is coming from the ECM. I checked both pins and they both have a lil over 9volts when the ignition is on. No change when pressing start switch. So, I'm lost right there. If I'm not mistaken, the relay should be activated from the ECM when pressing the start button. Does that mean I'm not getting a crank signal from the ECM? The relay is not being activated when attempting to start. Could it some kind of code like a crash code or Supplemental Restraints code that is not allowing the ECM to send signal to the starter relay. Attached is the starting system diagram.

I watched the video step by step. I wired the relay to a light bulb and the light came on indicating the relay was doing its job. Now I am back at not signal from the ECU to the relay.

I received the starter and relay today and installed it. I tested the starter motor and it's good. I still am not getting a signal to starter.

At first, I checked the fusible positive wire coming from the battery to the starter and I had voltage. Now I don't, so the fuse is bad. I ran another non fusible wire to the starter from the battery (I am going to replace the fusible wire). On the relay, pins 85 and 86 both read ground with the switch off. With the switch on, I am getting 11v on pin 86 and 3.4v on pin 85. The battery was reading 11.6v so it's on a charger now.

No, it still have the same voltage reading. And I did jump 30 and 87 and the starter engaged.

So, I was able to get back to troubleshooting. I decided to go to salvage yard and purchase a harness because the clips on the ECU harness were broken. I also purchased the fusible battery to starter wire. After installing both, I installed a new starter and ran voltage to it and the starter engaged. I then connected the wiring to the starter, and I am getting power to the starter, but the starter is not engaging. The person I purchased the car from told me that she kept replacing the starter and battery. So now I am wondering what is causing this. I doubt it's the brand starter I am purchasing. For I have past my return window. Should I purchase the starter from Volvo Dealer? Priced over 500$.

Here's a video of what's happening. I connected a tester to the starter signal wire, and it reads low voltage until I press brake pedal. When I press the start/stop button it's reading a constant voltage until I press the start/stop switch again.

Okay. I understand that but the starter is new. I did disconnect the wire from the starter and ran straight power to it and it did not engage. It did before I connected any wiring to it. So, I'm back to something that is burning out the starter. I am still getting voltage to the starter. I also ordered another starter. It is new, not remanufactured. I am waiting for it to come in. I just want to eliminate all other possibilities and not keep burning up starters. Thanks

Yes. It also turned when I first installed the new starter, I ran straight power to it, and it rotated the engine.

When I press the start button once to turn on the ignition. I am getting power to the starter signal wire. Still I installed another new starter and I'm ending up with the same result. I removed the starter and bench test it and it fail. So I'm confused on what is shortening out these starters. The starter should only get a signal when I step on the brake pedal and push and hold the start button, not when I push the start button without stepping on brake pedal. Am I correct?

I am getting voltage at both when pressing the start button.