I just changed the flasher on my 96 XLT to an electronic EP-27 so I can upgrade to LED's...
Mine was located behind the knee panel (below the steering column). It was clipped to a metal support bracket. It popped right off.
Had to get upside down on the floorboard & squeeze my head between the seat & pedals to finally see it.
OEM relay was blue, as was the connector... not 100% sure if the later year trucks have the relay in the same place though.