I understood that the 280sl didn't have the 1 second relay as standard but it was available as an option.
It was standard on the early 230sl.
How many solenoids are on your Injection pump?
If the wiring harness is new, could it be pre-wired for the cut-off solenoid that was on some 280 SL Injection pumps?
Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto