>>1996 turbo diesel...
>>
>>Am I supposed to turn the key halfway, then wait for the wait light to
>>turn off, then start it?
>>
>>Or, am I supposed to start it, then wait for the wait light to turn off,
>>then drive?

The wait light comes on as the glow plugs are being energized. The first 5 to 15 seconds (temp dependent) warms up the glow plugs and the pre-combustion chamber in the head. After you start, the glow plugs will continue to cycle in synch with the wait light until the engine is warm enough to run smoothly. It's possible to just drive away, but believe me, you will be doing your engine a huge favor by waiting 30 seconds to let the oil get distributed everywhere and moving before you take off. Every car ought to have a wait light, but most people are too impatient to wait till the engine is running smoothly, and they shorten the life of their vehicles by immediately jamming the power to a cold engine.

My routine is as follows; I get in and close the door, turn the key to the wait position, then reach over and put on my seatbelt. By that time the wait light is out, and I start the truck, then do my "preflight checklist", organizing myself and preparing to drive off while I wait for the engine to warm up. Once you get used to it, it's a moment of peace before braving the traffic....I find myself doing it in my other cars too.