I looked at the CD version, the print version, and at Alldata. Actually Alldata had the best display of what should be exactly the same drawing.
Look to the diagram that has A, B, C, D, E power arrows heading out of the bottom. above that is F13 Aux Fuse Holder Power Seats (Code B). Those two fuses are powered by K5 Power Seat Relay.
The seat relay has term 85 always grounded and looks to terminal 86 for control. Power comes to terminal 86 when the doors are open through either S17/7 or S17/10 Door Switches.
In the drawing the diode is shown wired such that when terminal 15R becomes hot (Ignition switch) power flows through terminal 2 (xF), through the diode and connects into the wiring for term 86; thus powering up the relay when the key is working or when the door is open.
The problem is that the drawing represents a number of variants over the years and the footnote states that the diode link is only applicable to model year 1989. Footnote 3 shows the new link as of 1990. The way it is drawn only connects the seat switches which would leave no relay power with the key on.
This may be as confusing as I have ever seen a MB drawing. I don't recall are there two door jam switches on that car? If not the switches are tied into the alarm system and door look pneumatics.
one interesting note on the diagram that I specifically don't understand is the intention of the dotted line going between pins 1 and 2 on the electrical center (F1).
Bosch Master, ASE Master, L1
33 years MB technician