This wire is a straight voltage signal, to enable the antenna amplification system within the module.
Just remember, the front is only for FM, not for AM. AM reception is only from the rear antenna.
As for the rest, the diversity antenna system is just that, diversifying the signal, to obtain the most correct and strongest signal for FM.
On hardtop, a standard signal receptive antenna is used.
Without this wire enabled, you will not have the optimized system working.