The roof aerial will provide better signal than a window aerial. It should be plug and play with the FM going into the cars wiring and the DAB going into your highway unit. You may need to by a new adaptor off ebay but that's just a guess as I don't know what connections the highway uses. I know the DAB aerial is a fakra but can be changed.
If you can't see any tabs on the glass then you will need a new rear window. I have the same as you glass will built in aerials but no tabs. I've contacted Pilkinton who manufacture the glass asking if they can supply the tabs but they said no and referred me to a glazing company. I did have the wiring near the pedal but that's only good for factory DAB, not your highway.
Have a look in the for sale section, I'm selling a roof mounted dab aerial which would be perfect for your needs.
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Link for the aerial below
https://www.vxoc.org.uk/forum/showthread.php?tid=2212
Sent from my LG G4 using Tapatalk
If you can't see any tabs on the glass then you will need a new rear window. I have the same as you glass will built in aerials but no tabs. I've contacted Pilkinton who manufacture the glass asking if they can supply the tabs but they said no and referred me to a glazing company. I did have the wiring near the pedal but that's only good for factory DAB, not your highway.
Have a look in the for sale section, I'm selling a roof mounted dab aerial which would be perfect for your needs.
Sent from my LG G4 using Tapatalk
Link for the aerial below
https://www.vxoc.org.uk/forum/showthread.php?tid=2212
Sent from my LG G4 using Tapatalk