the wiper control arm on the switch is snapped off on my car. I found one on ebay that says it will fit 78-79. were there any differences made to the 1980 switch / control mechanism that would prevent it from working on my car?

 

it has three levers. turn signal on left, wipers on right and cruise control on right as well.

 

I find it's useful to go on 928 Intl.'s or 928 Specialists sites to see what year cars are compatible for their parts:

http://www.mailordercentral.com/928intl/

and,

https://www.928gt.com/Default1.htm

Also, you can look at the PET on AutoAtlanta's site:

http://www.autoatlanta.com/porsche-p..._928_parts.php

That'll save you having to wait on someone to respond.