Not exactly what you were looking for but I'm not sure Ford let's you control the volume.
I'll preface this by saying I always use my seat belts on the road. With that being said, I use my truck on large job sites a lot and many times have to move my vehicle throughout the job site. Therefore, I turn off the driver's seat belt reminder so I don't have to constantly hear it.
From the owner's manual.
Note: The driver and front passenger warnings switch off independently. When you perform this procedure for one seating position, do not buckle the other position as this cancels the process.
Read Steps 1 - 4 before proceeding with the programming procedure.
Make sure that:
- You set the parking brake.
- The transmission is in park (P).
- The ignition is off.
- You close all vehicle doors.
- You unfasten the driver and front passenger seatbelts.
This switches the feature off for that seating position if it is currently on.
- Switch the ignition on.Do not start the engine.
- Wait about one minute until the seatbelt warning light switches off. After Step 2, wait an additional five seconds before proceeding with Step 3. Once you start Step 3, you must complete the procedure within 30 seconds.
- For the seating position you are switching off, fasten then unfasten the seatbelt three times at a moderate speed, ending in the unfastened state. After Step 3, the seatbelt warning light switches on.
- When the seatbelt warning light is on, fasten then unfasten the seatbelt. After Step 4, the seatbelt warning light flashes for confirmation.
This switches the feature on for that seating position if it is currently off.
https://www.fordservicecontent.com/...d=8431&vFilteringEnabled=False&userMarket=usa
- Switch the ignition on.Do not start the engine. How do you do that on a push start on/off ?
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