It is a gizmo that works with the ALDA and prevents it from overboost. It sits on the driver's side firewall and has plastic hoses connected with one nipple vented to the air. If it is bad and you have lost power, it is often the problem.

My 81 300SD lost all performance and would not go over about 30mph. I replaced it and the power magically reappeared. Search for switchover valve on the forum.

Will try to find a picture. Found one. This is the new style; note one nipple does not have a plastic hose, is vented to the air. (If you get the hoses mixed up, it will not give your performance back so take a pic before you remove the hoses.) As I remember this new one was installed completely upside down from my original switchover valve; not sure why they changed the design. But it really works great now and I have all the original pep.

Attached Thumbnails