I'm in need of help
 

I have a 2002 ml320,, I was driving down the highway and loss all power,, no lights, no brake lights, no emergency flashers.. got the truck towed home.. put a battery charger on over night.. next morning tried to start and won't start..
I put a new alternator in maybe 6months ago. I've also put a new crank shaft position sensor in maybe a year ago.
There is a ringing sound coming from back of engine, bye where the air intake comes into the engine. When I pull the stop lamp switch relay the ringing stops, plug in the relay the ringing starts and is flowed bye a few clicks and keep ringing.. I've tested the relay with a multimeter and it seems to be good, I've also checked the stop lamp switch it self and seams to be good.. and I put it back on bye the break pedal..
still nothing... I'm running out of ideas if anyone can helpPlease please let me know.. I desperately need this old girl back up and running lol.... Thanks for any and all help