TT(Aero?) levers

How do you route the cable on one of these brake levers, on bull horns that is...? http://www.chainreactioncycles.com/Images/Models/Original/34902.jpg

The cable goes between lever and bar, usually under the tape.

Depends on which bullhorns you have.
On something like a profile airwing there will be some holes and grooves to allow you to partially route the cable inside the bars, but with more old skool horns or something like Nitto then you'll have to stick it on the outside all the way, just between bars and tape.

When you've cut the cable housing to the right length and worked out how it's going to follow the curve of the bars, tape it down securely before you wrap them.

follow the curve of the bars on the inside of the bar rather than the outside ie back, but if needs must, whatever way gets you there.

If no holes then drill them in - about an 1" back from the end of the bars centre underneath, then about 2" away from the stem, and either side, job jobbed.

About a 1/4" drill is ok, and if possible give the casing a gentle entry shallow bend to go into the bars.

Put cables in from the stem end of the holes, otherwise from the other end you may never find it again!

As above, drill a hole 6 - 6.5mm and route outer casing through the hole, to the end of the bars. Postion lever and tighten allen expander bolt. Thread cable inner from bar end, job done.

Cheers El_Diablo, i was concidering this but didn't know if it would effect the strength of the bars, but if you've done it I presume it good?