It could be that your 124 cars does indeed have 2 fuel pumps. Many of the 124 cars have the M103 engine(single oevrhead cam straight 6 cyl). If this is your case, back the car up a bit on ramps. If the fuel pump/filter is located in the same place it is in the 88-91 300SELs, you'll find it just to the left of the right rear tire. It may be covered by a plastic shroud that's held in place by 3 small bolts/nuts. The 88-91 300-SELs have a SINGLE fuel pump. The filter is next to it.
I wonder if your 124 also has a single fuel pump? Once you have backed the car up on ramps, you can get underneath and see what your situation is.

Mike Murrell
'91 300-SEL