Heater Issues

[H]

Hello, I'm after a bit of advice regarding the way my heater controls are not working as intended.
When driving without the sidelights or the main beam lights on, the heater blows hot air when I require it . However , as soon as I switch either sidelights or main beam lights on then the fan speed increases and stars to blow cold air . In addition the heater control panel does not illuminate ( my car is the Zetec without the climate control and so has the three rotating controls, one for the temperature, one for fan speed  and one for direction eg screen).
I know its not going to sound good, but a thump of the trim around the heater temperature control knob results in the panel illuminating (temporarily) and the heater blows hot air as required.
It may be that there is some form of short behind the heater control panel and if it was thought that this is the best place to start how do I go about removing the trim to get to the back of the control knobs.

[Chrispb]

Not tried this myself but has been mentioned before about disconnecting the control panel then reconnecting seems to cure faults like that, would think disconnecting the battery would do the same, worth a try I suppose.

[H]

OK thanks what is the easiest way to gain access  the rear of the control panel.