This topic has been discussed many times at TBN,
it's a simple system, but you are right, not covered in OP manual.
The system only works while the key is in the "crank" position. So, in order to get a preheat, you need to either move the shifter lever into gear, or turn the pto switch on, and then turn the key to crank. The engine won't turn over, but the preheat will work. AFter a few seconds, switch whatever switch you used to cancel the starter engagement back to it's normal position and start the tractor, with less cranking and less smoke. Easy as Pie!
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