We recently replaced the cylinder head on my 1984 300SD and did so successfully I might add , but that's another long story. In the process, however, we discovered that the overboost protection circuit does not exist. The boost pressure sensor (see attached picture of same component, new) is installed on the intake manifold (or boost air pipe per MB), but there is nothing connected to it. As I understand it, (see attached diagram of turbo operation) when boost pressure is monitored to exceed 1.1 bar, this sensor provides an electrical signal to the switchover (aka changeover) valve which interrupts the boost pressure line connected from the banjo fitting at the intake manifold to the switchover valve and then on to the ALDA, thus removing corresponding fuel enrichment needed for additional boost. My real question pertains to the location of the wire that would normally connect to the boost pressure sensor. I'm assuming that it originally connected through the passenger side of the firewall into a harness to which the switchover valve is currently connected, but I find no evidence of such a wire. I've only owned the car for the past three years and haven't had a chance to really work on it until recently. In addition, I have no knowledge of what occurred or didn't occur for "maintenance" prior to me. I would assume that at some point in the past, the sensor malfunctioned so someone simply disconnected it and went ahead and removed the wire. Can someone please tell me how it is supposed to be set up/dressed out? I would eventually like to tweak the boost pressure control valve to achieve turbo boost that is something closer to 1 bar, but I will not mess with it until after optimizing the ALDA (at which point it may not even be necessary to mess with the turbo) and certainly not as long as I have no overboost protection...

Thanks,
-Ken

Boost Pressure Sensor:

http://ken.kdharris.net/kdhbenz/turbo/boost-pressure-sensor.jpg

Turbo Operation

http://ken.kdharris.net/kdhbenz/turbo/turbo-schematic2.jpg