The glow plugs are controlled by the controller bolted to the rear of one of the heads. It senses key on sequences and engine temperature. There is a coolant temp swwitch that disables them when the engine is warm. Replacement switchs are just a jumper so that the glow plugs run even if the engine is warm.
Another coolant switch controls the fast idle and cold injection advence. There is also a separate sensor for the gauge.
The lift pump relay (under cover on firewall) controlls the lift pump while he starter is engaged. The oil pressure switch on the rear of the block below the driver's side head controls it while the engine is running. They fail frequently.
There is no PCM. If you have an automatic, there is a transmission control module, but it has no connections to the engine beyond the throttle position sensor.
The Constitution needs to be re-read, not re-written!
If you can't handle Dr. Seuss, how will you handle real life?
Current oil burners: MB GLK250 BlueTEC, John Deere X758
New ride: MB GLS450 - most stately
Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510