Randy......I was the guy that started a thread on this subject on another board.
I have a 2010 - 2520 and as you state, it says nothing in the manual about that light on the dash. It doesn't show at all on the JD picture where it supposedly describes the lights and indicators on the dash.
I do have the light on mine as well, although it is obvious by some of the responses on the other thread, that there are a lot of others that do not have this light on their dash.
There is a lot of confusion on this light/no light thing, and the only conclusion I support is that as Spudland Dave indicates, somewhere along the line, JD made a change to the engine in the 2520 models, and didn't update the owners manuals to reflect the changes.
It sounds like your 2008 model is the same as mine, so it stands to reason the change was before that. Who knows, maybe it was a running change and they could be using different engines within the same model year.
I really think JD should provide an addendum to their operators manual. Unless a dealer specifically explains the starting procedure, how would anyone know to wait for the dash light to go out before cranking assuming of course they have the light. I also have an X495, and it's the same thing, wait for the light to go out and then fire it up.
I've tried my 2520 both ways, and it will start by just cranking on it, but it starts a lot faster if I wait for that light to go out. There was even a guy on that other thread that thought his 2520 started great until he tried waiting 15-20 seconds in the "on" detent and then cranking. He was quite startled by the improvement. I think he was one of those that had no light on his dash, and he found a noticeable improvement by waiting that 15-20 seconds.
I don't know, but wouldn't the pre-heater thing be the same? Meaning there should be a pause in the "on" position before cranking to allow the pre-heater to do it's job. If so, you would think all manuals would at least explain the need to pause in the "on" position for a few seconds, light or no light.
Sounds like waiting will save wear and tear on the old starter motor. JD should do something to correct this. I think there a lot of folks out there that don't know the proper starting procedure on this tractor.
REV