@Jsrrags on the Beck Spyder wiring (and maybe others) you can make a switch like suggested by @Alan Merklin however you also have to add a diode to the front turn signal that is on the "in" side of the switch otherwise your brake lights will backfeed to one front turn signal. This is different from a Speedster because the Speedster has 3 separate elements to control 3 functions, while the spyder has to do so with a single dual element bulb.
For the horn there are several ways. The 2 most common for me are: #1: I like to make a derin insert for the turn signal switch and then rob the horn finger off the old turn signal unit and make a custom insert that retains the horn isolation just like factory. #2: look at how it was done on a 356 (and I think old beetles) where you have an isolated copper ring around the column (spaced away form he column with plastic) with an attached wire that runs to your horn button, and a spring loaded copper ground contact that attaches to the column tube behind the dash and "rides" the isolated ring. Method #2 can be done with old 356 and VW parts, but also requires removal of the column tube and column for fabrication.