The one in my CD has been bypassed by a PO, the engine hasn't blown up yet, as some folks will scream at you that it will.
The one in the SD is connected.

Well, I guess that I will remove the top endcap.

The top endcap is vented. It's just there to prevent debris from falling into the valve. You don't need to remove it unless you plan to use the port for another task.

Pholway, try hooking that solenoid up, the way it is supposed to be, then feel the performance of your car disappear before your very eyes. Truly a magic box. Then, you can start to diagnose which part of that overboost protection system (which the PO bypassed ) has gone bad. My 300sd is currently configured the same way, (line from banjo bolt hooked directly to the ALDA) and I am working on figuring out which part is bad. Solenoid/valve or sensor. Brian has had some great advice about how to do that, check thread - Black smoke, not enough

If the performance deteriorates when the solenoid is connected...........the solenoid is the culprit............nothing else.

However, the overboost system can fail to function properly and prevent overboost if the pressure sensor or the overboost solenoid are clogged or non-functional. A failed pressure sensor won't affect the performance of the vehicle..........but it can fail to prevent an overboost condition.

Thanks Brian. Again.
I think I might just use that as my signature.