Looks like your truck falls in the range of a recall for a defective cruise control brake disconnect switch. The switch is mounted on the brake master cylinder. The issue is that a seal fails and allows brake fluid to reach the electrical components within the switch. While this is an annoyance it can lead to a fire originating at the switch itself. I have worked several of these fires. Since the switch is on the brake light circuit electrical power is always available to the switch. If I were you I would check with the local Ford dealer for more information.
Here is a link that can give you more information. It was written by an attorney who handles fire subrogation cases. The information is now a bit dated but it still applies.
https://www.cozen.com/admin/files/publications/Motor_Vehicle_Fires.pdf
For additional information do a Google Search on Ford cruise control disconnect switch fires