Yes, in the rear behind the gas door - it should hisssssss, some people guess that the sound is exhaust. Have someone put the key in while you put your ear down behind the rear passenger side tire, when the key goes to the ON position, it should cycle once and "hiss" about 3-4 seconds. If this does not happen, you're fuel pump is not working - check the fuses. If they're blown, it's probably a temporary fix as the pump is probably getting old and shorting them out. I had this on 2 of the 4 W126 cars I own(ed )- usually with between 150k and 175k miles.
I read what you wrote before, and your starter sounds "normal" right? Just the car is not starting like it would not be getting fuel?
2003 S500 Black/Charcoal
1990 560SEL 61k Arctic White/Grey
1988 420SEL Black/Palomino Sold @ 85k
1987 420SEL Midnight Blue/Grey
1986 420SEL Diamond Blue/Grey
1983 380SEL Champagne/Palomino