When working on Older FORD products (OBD-1) you are told that if the ignition module is suspected, swap it with a known good one...you are also told that 8 out of ten so called "new, replacement" modules from the auto parts store are defective, right out of the box...soooooo, how do you swap in a "known good module"? Simple! Go to the auto parts store, buy the module, and, before you leave, hook up this tester! I did, and found that out of ten, the auto parts store had five defective ones in stock! The counter guy has asked me to bring this tester back once he orders more modules! If that isn't a testamonial, I don't know what one is!