Centaurus....
I checked the wiring schematics for one airline's 737-300's (P&W-engined) today and there was no input from the flaps to the Fuel Control Unit solenoid.
I don't think my findings prove conclusively that your -300 aircraft are the same. I think you need to contact your engineering department to find out the specific details of your own aircraft. There may be variations between airlines and between aircraft. On another airline's 747-800, I saw that there was a flap input (at least to the EEC... what the EEC did with it, I couldn't tell by looking at the diagram).
Regards.
Q.