http://tunertools.com/proddetail.asp?prod=TXS-KNOCK

That would be the knock light and if you do some searching people list the knock sensor you can use mostly it runs off a bosch 2 pin ev1 style sensor. From what i have found people run sti and wrx sensors.

I would tune it with the 98 then only run the 100 so this way you can make a safety buffer to keep knock down under. lol