Switch/sensor on top of IP

[Nevadan]

What is the function of this sensor/switch mounted on top of the injection pump? I think the wiring harness is somehow connected to the turbo warning light in the dash. I know for sure the wiring harness connects to the turbo pressure sensor mounted on the passenger strut brace (second picture).

[v8volvo]

Those are all part of the EGR system. It has vacuum and electrical switches on the throttle lever as well as a thermo vacuum switch installed in the "tee" where the return hose from the cold start thermostat runs into the heater hose connected to the t-stat housing. The solenoid valve in the second picture is commanded to open or close based on what the throttle position switches are doing, and the thermo switch does the same based on coolant temp -- I believe the idea is that the system should not operate at idle or WOT, or on a cold engine, assuming all components working perfectly.... which they very likely are not. There is a greenbook that describes the way it is supposed to function, but IMO fooling with it is a waste of time... Pretty primitive system with no feedback or electronic control means who knows if it's ever doing its job correctly or not, and the mechanical control logic can't be too well-optimized even under the best of circumstances. IMO EGR w/o MAF and MAP sensors and full computer management is a mistake. (Some argue that it's still a mistake even with all that...)

Probably better of taking it all out or at least disconnecting it, saves hassle and clutter and potential for problems, and motor is better off without it (can help fill the intake with sludge among other issues). If you remove or disconnect it, just make sure to plug the vacuum supply hose to the EGR system, otherwise your brakes and HVAC controls will be affected...

[Nevadan]

I'm in full agreement with disconnecting all of it and will do so. One of the reasons I bought the vehicle was for the simplicity. The wire clutter and physical mechanism would be better off gone anyway. There was excessive carbon/sludge in that small aluminum manifold piece and I will clean the full intake manifold during my cam replacement work.