I have a GE exhaust fan with a heater and light.there are two cables one on each side of the fan housing unit In one cable there are two wires(black and white) In the other cable there are three wires(red,black and white) The fan wire connection box has seven wires(three white,one red,one black,one yellow and one green). The same type of fan was here before. I have one switch for the three functions(fan,heater and light) how do I connect these wires together?

Need to follow wiring of the old. What you said does not seem right, the cable with white and black should be the cable going back to your circuit breaker, the red, black and white is either going to a three way switch or they control fan, heater and light. You can get a switch that has three toggle switches in it to fit in a single gang box, that will only work if your switch has the red, black and white wires inside the switch box. You mentioned the wires in the fan housing unit but not the switch. As for the new GE exhaust wires I would say the three white are the neutral wires one each for the fan, light & heater, as for the red, black and yellow they will more than likely be you 120VAC supply to the fan, light & heater, the diagram with the unit shoud ID what the wires operate. The green as with most appliances is your grounding wire, it should go to the bare wire in the cables you mentioned. I hope this helps.

Remove switch from switch box.

What you should find is two 2-wire cables (black and white) and one 3-wire cable (black, white and red).

All neutrals (white) should be connected with a wire nut. The black of the 2-wire cable bring power to the switch should be connected to the common of the switch. The black of the other 2-wire cable, and the black and the red of the 3-wire cable should be connected to the switch terminals. Make a note of which wire is connected to which switch.

Mark the 3 white wires of the fan as A, B, and C. With a meter check for continuity between A and B, A and C and between B and C. Put a bulb in the light. Check for continuity between each white wire and the black, red and yellow wires.

Check instructions to see if the fan, light and heater wires are identified. It is probably black is light, red is heater and yellow is light.

Post back what you find.