Follow the wiring. If this was a modification you will find a small box somewhere that controls it. It really doesn't matter what you do with it as its only affect is through the add-on frequency valve. The wiring won't be part of the original harnesses.
As to the valve, you CAN NOT just bypass the injector. This would dump all the control pressure. Look at the piping and realize that the idea was to dump a controlled amount of control pressure into the fuel return. The fuel return is at the fuel distributer. The best solution is to remove the rig. Another solution would be to securely plug the line (NO fuel flow).
Bosch Master, ASE Master, L1
33 years MB technician