Chances are it's in the trunk
If it's like my 300SD the electric pump is in the trunk on the right side by the spare tire. My wife has an '86 300E and it's also in the trunk, so I'd suppose yours is there as well.
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan