My friend put new headlight assemblys in his S4 'vert. I havn't looked at it but apparently his headlights work but when he turns on his highbeams the headlights turn off but the highbeams dont turn on. Im guessing this is just a wiring problem but the wiring is pretty straight forward. Any idea could this be?

 

If I remember right, there is a high beam relay that might have gone bad.

 

It seems very unlikely that swapping the housings would causes relay failure. If they were working okay before the swap he's probably put the wrong housings or bulbs in. They should be H4 housings and bulbs.