Don,
This is based on how our Thunder works, your Marquis maybe different. Here are a couple things that you can check. In the multiplex closet, on the righthand side, there are three purple Bosch relays mounted on a board that are controlled by the fan (multiplex) switches. These relays do not provide any power to the fan but rather, when closed, complete the circuit to trigger the fan controller to open the fan cover. You should hear the relays click when the multiplex switches are turned on, the relays will be fairly warm when energized. Check the relays and connections on the PCB. You can test the fan circuit and controller by pulling one of the relays and jumpering the normally open terminals. If the circuit and fan controller are good the fan cover should raise.