The Restraints (airbag) Indicator Lamp is so important that Ford added an audible backup to warn you if it stops working. That is the 5x5 beeps that you hear after startup and later on. Repair the Restraints Indicator Lamp (most likely a bulb failure).
If the Restraints Indicator flashes after it's repaired, count the flash pattern and post it.
2003 FX4 Level II, Supercharged 5.0L V8, Headers, Duals
BW4406 manual transfer case, Aussie Locker, Torsen L/S, 4.10's
Bilstein 7100 rezzies, Cadillac/Mustang rear discs, Duff traction bars
Keypad Entry, Lock LEDs, ABS switch, sway bar discos
Heated seats, Explorer EATC, Trip Computer and consoles
2003 XLT 2.3L M5OD-R1 reg cab beater, 2011 Taurus SEL, 2016 C-MAX Energi Plug-in Hybrid