I see posts from members in cold climates indicating that they let their glow plugs glow for X # of seconds before they crank the starter to fire their baby up. Is there some way to set the length of time the glow plug burns, or is this just a shortcut way of saying that the key gets returned to the 0 or off position and then turned back to the position which fires the glow plug repeatedly until they reach the time indicated before cranking the starter?

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1986 300SDL
1988 Monte Carlo SS
2002 Avalanche
2003 100th Anniversary H-D Dyna Wide Glide

To my knowledge the glow plugs come on with the key in the GP position, the GP dash light goes out after a period depending on how hot / cold the engine is, but if the engine is cold the dash light goes out after say 10sec but the GP circuit actually stay on for another say 15sec even after the engine is running. On my 92, 300D the lights will brighten up and you can hear the CLICK of the GP relay kicking out when they do cut out after starting eng, whilst eng has been running for about 15 sec. There also must be a temp. sensor to know for how long to run GP if the eng. has temp. in it, because the GP time varies if eng. is hot or cold.