defrost board

hi, im installing a defrost board on a heat pump, what is the letter D and it has a purple wire going to the defrost board actually am installing the inside coil and outside coil but i came to this letter D and im not sure what wire to connect with the purple wire. this wire is together with the R,Y,O/B that are going to be conected with the wires going to the t-stat.:confused:

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that's the banner, I'll bet if you were to bother reading those rules you would see 1 stating NO DIY, I could be wrong---wouldn't be the first time.