I never worked with OP17 and i do not have the software installed anymore so in Protool this should be something like this:
system->Areapointer
add-> Led assignment (e.g. MW10)
then:
System->Screen/keys
Goto the K-key (General) and choose what bits you will use to control the led on the key.
bit n+1 bit n led
0 0 off
0 1 2 Hz
1 0 0,5 Hz
1 1 on