So a few years back i built a knock light using this circuit here.



It lets you build a cheap knock light system great for tuning. It runs off a knock sensor from 1980 to 1996 Dodge and Plymouth vehicles. Try a NAPA Echlin DKS100 knock sensor. It has a 3/8 inch coarse thread stud about
a half an inch in length.

Here is a pic of the sensor.



Once you have built the circuit you need to set the pot so that it only light up and goes off if you knock or ping.