Okay I looked it up on my F250 repair Disc and found this about the BCM:
Principles of Operation
The Steering Column Control Module (SCCM) monitors the multifunction switch position. When the multifunction switch is in the LH or RH TURN position, the SCCM sends a message over the High Speed Controller Area Network (HS-CAN) to theBody Control Module (BCM) indicating a request for the LH or RH turn signal.
The BCM sends a voltage signal to the hazard flasher lamp switch. When the hazard flasher switch (a momentary contact switch) is pressed, the voltage signal is routed to ground, indicating a request to activate or deactivate the hazard lamp function.
When the BCM receives a request for a turn signal or the hazard lamps, the BCM supplies on/off voltage to the appropriate turn lamps.
The timed on/off cycle for turn lamps is determined by the BCM and is set to flash approximately 80 times per minute if both the front and rear turn signal lamps operate correctly. If an individual turn signal lamp is inoperative, the BCM fast flashes the remaining turn lamp approximately 160 times per minute to indicate a bulb outage to the driver.
There is no bulb outage indication for the exterior mirror turn lamps.
The timed on/off cycle for the hazard lamps is approximately 80 times per minute regardless of bulb outage.
The BCM bulb outage is configurable and can be turned off for the front or rear lamps. This is to accommodate vehicles that have been outfitted with rear LED lamps in place of the traditional incandescent bulbs.
The rear turn signal lamps share functionality with the rear stoplamps.
The multifunction switch is a momentary contact switch, with 2 detents for the LH TURN position and 2 detents for the RH turn position. When placed in the first detent, the corresponding turn signals flash 3 times and turn off. When the multifunction switch is moved to the second detent, the turn signal flashes until the steering wheel is turned in the opposite direction (based on input from the steering wheel rotation sensor), the multifunction switch is moved to the second detent a second time or the vehicle travels farther than 3.2 km (2 miles). The BCM monitors the steering wheel rotation sensor and the multifunction switch input to determine when to cancel the turn signals. The BCM monitors the distance traveled to determine if the turn signal should be turned off.
