What is the black box attached to a rear view mirror on my 2007 Ford F150 truck?

That black box attached to your 2007 Ford F-150's rearview mirror is most likely the OnStar module (if your truck was equipped with OnStar) or a similar telematics control unit 。 これらのユニットは、緊急サービス、リモートロック解除、車両診断、およびナビゲーションなどの機能のコミュニケーションを処理します（トラックが持っていたオプションに応じて）。

It could also *possibly* be a less common aftermarket device, but the OnStar/telematics module is the most likely culprit. If you can provide a picture, I might be able to give you a more precise answer.