Unlike newer Rangers that have fuses, your son's 94 uses circuit breakers for the headlights. They are flashing off and on as the circuit breaker opens and then automatically resets itself. I suspect that one of the breakers is bad or there could be a problem with the headlight switch. The headlight switch on 94 and earlier has a reputation for failing at high miles.
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