I think you should be able to achieve what you want with a bit of tinkering.
Here is an example of the lights section from a plane I am working on at the moment in which the cabin and panel lights are switched separately:
[LIGHTS]
//Types: 1=beacon, 2=strobe, 3=navigation, 4=cockpit, 5=landing
light.1 = 1, -5.42, 0.00, 1.96, Ants_aa12_beacon
light.2 = 2, -7.4, -11.6, -0.18, fx_strobe
light.3 = 2, -7.4, 11.6, -0.18, fx_strobe
light.4 = 10, 3.62, 0.00, 1.31, Ants_aa12_vclight
light.5 = 7, -13.5, 0.00, 0.00, Ants_aa12_engineexhaust
Light.4 is the cabin lighting, = 10 makes it the cabin lights and attaches it to the cabin lighting circuit.
Compare to this code from the default 737:
[LIGHTS]
//Types: 1=beacon, 2=strobe, 3=navigation, 4=cockpit, 5=landing
light.0 = 3, -24.20, -56.60, 3.90, fx_navredm ,
light.1 = 3, -24.20, 56.60, 3.90, fx_navgrem ,
light.2 = 2, -71.32, 0.00, 5.92, fx_strobeh ,
light.3 = 2, -25.00, -57.20, 4.20, fx_strobe ,
light.4 = 2, -25.00, 57.20, 4.20, fx_strobe ,
light.5 = 2, -7.55, 0.00, -5.50, fx_beaconb ,
light.6 = 1, 2.00, 0.00, 8.70, fx_beaconh ,
light.7 = 4, 47.60, 0.00, 3.00, fx_vclighth ,
light.8 = 3, -29.50, -56.60, 3.70, fx_navwhih ,
light.9 = 3, -29.50, 56.60, 3.70, fx_navwhih ,
Light.7 is the cabin light and = 4 attaches it to the panel light circuit.
Now, developers must use the panel light circuit to get gauges in the virtual cockpit to light up, it is just the only the materials work and there is not a lot the developer can do (unless they want to try some really tricky tricks). So, for most aircraft out there turning on the panel lights will also turn on the gauge light.
But, most aircraft are also setup so the virtual cockpit floodlight (ie fx_vclighth) will turn on with the panel lights.
You can change this.
Using the 737 example above if you change
light.7 = 4, 47.60, 0.00, 3.00, fx_vclighth ,
to
light.7 = 10, 47.60, 0.00, 3.00, fx_vclighth ,
Then the light effect will now be on the cabin lighting circuit.
Now when you turn on the panel lights the gauge lights will come on but the overhead light won't.
So how do you turn on the overhead lights. Well, the default 737 doesn't have a switch for this (at least on that works) and you can't assign a key command to cabin lights like you can with panel lights. Or can you?
This little trick I learnt from Bill so credit to him.
If you manually edit the this file:
Users\username\AppData\Roaming\Microsoft\FSX\Controls\Standard.XML
You can add in an entry to toggle on/off the cabin lights.
Drop something like the following into the standard.xml (I don't think the place matters but you can put it next to the Panel_Lights_Toggle entry if you like)
(Entry)
(Key)SHIFT+P(/Key)
(Down)TOGGLE_CABIN_LIGHTS(/Down)
(/Entry)
You will have to replace each ( with < and each ) with > as this forum isn't letting me show the code (even if I put code quotes around it).
Code:
< Entry >
< Key >SHIFT+P< /Key
<entry>< Down >TOGGLE_CABIN_LIGHTS< /Down >
< /Entry ><entry>
So it looks something like the above. I've had to put spaces where they shouldn't be to get the code to display on the forum. Once you open up standard.xml you should be able to figure out how it should look.
</entry></entry>