My 84 300 turbo d won't shut off when I turn off the key. I have to open hood & hit engine stop lever.

I obviously am not familiar with the application here but petrol engines have an electrical ignition system that can simply be turned off to stop the engine. However diesels have super high compression that causes the ignition. Diesels with mechanical fuel systems will continue running until the fuel is shut off or the engine is stalled. The fuel is usually supplied to the injector pump through a solonoid valve where an electrical supply is needed to open the valve and the valve springs shut when the supply is removed. The fault is 90% in my mind associated with the this fuel shut off valve. However there is another way that a diesel engine can find fuel to not allow it to stop. A turbo seal failure can atomise engine oil into the inlet manifold and the engine will continue running until all the is used up.

The switch is defective/shorted. Remove the bulb

If you messed with the ignition system on the vehicle to get it started without a key then you disconnect what you did to now stop the engine.

Check out the cable connection between the latch and your internal latch control. Till you locate the problem I would suggest tying down the hood with some sort of strap so it does not pop open at speed.

Go to hood and push down on it and try release lever,if still doesn't open,then go back to hood and release lever at hood and try to raise or push down to lock.

Is the Check Engine Light on/ If yes, go to AUtozne & get codes read and report them here.

Also, try cleaning the MAF sensor and throttle bdy with spray carb cleaner.

Check for 40 psi of fuel pump pressure. Can you hear pump hum for 5 seconds when key is turned to ON? Listen at tank at rea of car, pump is in the tank.

While you are pulling out on cable have someone hit hood with each fist on front of hood near grill left & right of center at same time.

low fuel pressure. have pump tested

change the switch in the top back of the injector pump ,it has one wire running to it and should be at the back of the pump where the fuel line goes into pump housing