Turn signal stalk switch...
 

'88 Carrera Special Edition:

Everything on the turn signal stalk works, Left, right, low/high, except headlight flasher.

Circuit 30, horn, hazards and parking lights all work with key off/out.

Unless advised otherwise I'll tackle the turn signal switch assembly first.

check the relay for the flasher.....you may need to remove the wheel and switch cowl

No relay involved according the schematics provided by our host. Headlight flasher power, circuit 30, goes directly to the turn signal switch assembly and from that directly to the high beam connection.

I'll have more time to look later, but there is a thread with photos about cleaning the contacts. That is likely the problem. The contact when you pull back is likely dirty/corroded. Getting the steering wheel off is fairly easy (Need 27mm deep socket). I just had a little trouble getting it back on. (Nut is hard to thread back on).

....I meant the contacts...sorry, relay was the wrong terminology.
I had to adjust mine when the high beams would come on when I went over a bump in the road

Small matter, but I needed to use a 27mm short socket with an extension. There is a plate on mine ('87) partially obscuring access to the nut and a deep socket is too fat to get a clear bite. Sorry I don't have a picture to post but if you pull off your horn button you will see if you have good access or not.

Here's the link I was referring to... Hope that does it for you. Let us know.

http://forums.pelicanparts.com/porsche-911-technical-forum/248149-turn-signal-switch-quick-fix-pictures.html