According to Max BMW this is the "Hazard Warning Relay" 61 31 1 358 194. It is 4 prongs. It is taller than a standard size relay, most any other relay. And it has a clip on the back so it can be attached to the place in the headlight shell made for it. It fits 1974 to 1980 Airheads.
It is possible to make the system work with another relay but I forget now what it is you loose. It is probably the way to go since the OEM part is so outrageously priced.
Cleaning is an option, if you are lucky. It may or may not work but if nothing else is fixing this problem I guess you have nothing to loose by trying to fix the one you got.
There is more info on Snowbum's site. If you need help finding the exact article or don't know what I'm talking about then I'll give you more of an explanation. Snowbum's site has tons of useful info but I'm one of those that tires of trying to make sense of it sometimes. I count Mr. Snowbum is a personal friend. I don't know if he would say the same thing about me. But he can really ramble on sometimes tho.