I can confirm that a single inlet pump will work on a car that originally had a dual port pump. (w126 and w124's)
My 420sel has the lumbar driver seat, and the dual hookup pump.
The connections are the same between the single and dual pump. the only difference is, the in the straight 3 wire plug that feeds power (not the round 3 pin from the door lock switches). the (pressure) side of the pump is activated from the center pin where there's another wire. But the single and dual pumps will interchange and plug in.
When I first got my car, I discovered that neither the door locks or the lumbar seat worked. Upon closer inspection, I found the pump and circuit board totally burnt up inside the case.
I picked up a single pump model from the wrecker, plugged it in, and I had door locks
. But one little problem. the pump would continue to run for about 30sec after either a unlock or lock. Indicating some type of air leak.
This is a good tidbit to inspect for those grabbing these aged pumps from 20+ year old cars. Because it was a super easy fix.
I determined that the pump was leaking internally, so I opened up the pump, and determined I had a leak on both sides of the bellows plunger that tells the pump if it has reached full vac(to lock) or full pressure(unlock). I disassembled, and fitted 2 small o-rings to either side of the plunger shaft to snug up the seal. Having a properly working system saves a lot of wear and tare on the motor.
Also when in there, clean up the contacts for the activation relays, you will be surprised how dirty it gets inside these pumps. This will save you hours of headaches for when your trying to mess around with your door lock switches, thinking they are bad, and the pump must be good. LOL
Wire in one of those cheapie remote door lock moduels into the pump, and your set! One of the best mods ive done to date!
Pump has been running great for 2+ years!