I have a fahrenheit 240 electric baseboard heater. I went to install them and noticed that the only open wire in the wiring box on the heater is a black one, the red wire is fixed into a safety device. I have a white, red, black, and a ground wire. How do I wire this heater?

You need to look at the thermostat to determine the wiring control. Is this a 120 or 240VAC heater? What does the panel say. Brand new?

Having red and black in the heater implies it is 240 volts.

Sounds like you have 3 wire cable plus ground, use the black and red of the cable from a 2 pole circuit breaker in the panelboard, to the 2 pole thermostat, and continue onto the heater and connect red and black of the cable to the red and black of the heater.

Be sure to connect the ground at each location, panel, stat, and heater.