DIY Knock light (radio shack parts)
 

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

http://www.gnttype.org/techarea/proj...ck/circuit.gif

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.

http://www.gmcmhphotos.com/photos/da...um/59_p519.jpg

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.