Tom, You'll have everybody tut-tutting if you do as you suggest and drill a hole in the bar and thread the wire through. Frankly, I doubt you'd ever regret doing it that way as the bar (I'm assuming it's the FIA type with diagonals) is probably the strongest part of the car and if ever (dread the thought) it was called into 'service' would survive better than the chassis it's bolted to, but that's just my view. There is an alternative however, which is to bond the cable to the bar with a bead of Sikaflex or whatever. Done carefully this can look ok. Ezzer