As the switches return to their original position, you need something to remember whether the light is on. It is likely that the foglight switch has two contacts, one for up and one for down.
You could disconnect the switches from whatever they are connected to at the moment. You would then need to have a latch or microcontroller or something to store the current state.
This is likely the route that I need to take.
Alternatively, you could leave the current electronics, and run a relay from the foglight outputs. You might need a resistor to fool the car into thinking that the lights haven't failed.
My car aint that advanced, lol. Bear in mind we're working with 70's automotive electrical technology here, and trying to shoehorn 90's switching arrangements into the mix.
The current system uses mechanical switches, which flip a relay to turn the fogs on.
This works for both front and rear lights.
I suppose the way I envision it working is...
Side lights on - powers the circuit to allow the fogs to come on when the appropriate switching has been achieved.
1. Rotate the fog lamp switch up once - activates the relay for the rear fog lights
2. Rotate the fog lamp switch up again - activates the relay for the front fog lights
3. Rotate the fog lamp switch down - deactivates the front fogs lamps
4. Rotate the fog lamp switch down again - deactivates the rear fog lamps
The key element being that if only the rear fog lamps have been illuminated, then the down rotation of the switch needs to deactivate the relay supplyinf power to the rear lamps. I'd tried designing a circuit with transistors and relays, but in reality it's been that long since I did any of that type of electronics I was just getting myself confused. In terms of the practical soldering it all together, I am not in the slightest phased by it, so long as I have a workable circuit diagram to go off. Thankfully this isn't a "critical" circuit, so failure at any point is not going to be life threatening (say like with the main lights)
Thank you for hte responses so far, at least it's giving me a chance to clarify what I need to do