With the h15 high beam bulb doing 2 jobs is it plausible that if it was changed to an led variant that the reduced voltage that dimly illuminates the halogen version would dimly illuminate the led variant. 

 I've used various anbus friendly h7,h3 and H1 bulbs in MK2 Octavia and MK1 Fabias before with varying levels of success,and led t10s  but not these h15. 

The two functions are not achieved by dimming...

 

Take a look at a H15 bulb, there are two separate filaments, one for each function 👍

9 hours ago, langers2k said:

The two functions are not achieved by dimming...

 

Take a look at a H15 bulb, there are two separate filaments, one for each function 👍

That makes sense now. 

 I haven't removed the bulb yet but that would explain the 3 pins on the bulb 👍