crank sensor location

I have a 1988 audi 90 quattro and I'm not sure of the location of the crank sensor. I think it is mounted on the tranny where it mounts up to the engine. The problem is that there are two sensors located there, one is a little bit higher up to the left. Wondering if it is the speed sensor? Anyway I'm not sure how to install the crank sensor. Any help would be greatly appreciated.