Bit difficult without a picture but the three most likely things are the indicator flasher unit, hazard lights flasher unit, voltage stabiliser. Can’t think of any other electrical bits I have found hiding behind my dash.
Andy
Ah, try that could br the resistor that gives the fan two speeds, if I am not mistaken. Forgot about that before, should look similar to the ballast resistor on the side of a coil and pretty much performs same function. Does one of the wires from it go to the heater fan?
Andy
I agree that it is the resistor for the 2 speed fan & that it gets hot. That is why it should be screwed to the metal case of heater box. I would be tempted to put some therrmal paste on the joint as well…