08E63AMGboy

So driving home the other day and my car suddenlynlost all power and all the lights came on the dash. Power steerring locked up the whole nine. Could crank but no start so had to be towed. I did my research and saw that the culprit was most likely a faulty cps. But upon changin it after having a hellacious time getting to it, still same result. Car will turn over but wont crank. Not throwing any codes. Only indicator of any problem is my battery is seeming to not hold a charge due to my command saying battery too low for ignition. Also been getting a brake wear light on dash even tho they seem to be in good shape. Anyhow, Took it to autozone they charged it right up said it was fine. Put it back in and the car still wouldnt crank, watched voltage on the dash while cranking and it was around 9 volts so idk. Ive heard it can be this fuel pump relay but on the forum boards i see alot of people saying its on the right side of the car in the trunk. Ive only found it on the left side in the fuse box near the navigation. Has the exact part number for the relay. 1st one from the bottom all black on the far right wall. Just wanting to make sure thats the right one. And any suggestions would be greatly appreciated!

Solo wing

Get a gauge and read the fuel rail pressure with ignition on (pump primed).