Thexton THE404 Spark Tester

And actually it works better than my last one. The gap markings are clearly marked and was able to test coils as per warranty standards just fine. The glass tube makes the spark extremely visible for recording / photo purposes.Alligator clip is strong, I usually clip it to an ear of the engine block or alternator mount or something. No issues with grounding out the coils and is exactly what you pay for.Size is about the same as an ordinary spark plug. I have two of these in my box and haven't managed to break them yet. Definitely worth it.

I used these style spark plug testers at school. they are EXCELLENT! You can adjust how big you want your spark to be, which easily helps you determine if your coil packs or distributors are getting enough voltage or if your spark plug is bad.Long story short on how to use this tool: You unplug your coil/spark plug wire (depending on the type of ignition system of course) and connect it to the end of the tester that looks like the top of a spark plug. The piece that has an alligator clip just clips onto any part of the car that is metal in order to create a ground. Once it's hooked up, start your car. If you're able to get an arc going across the points in the tester, especially when it's adjusted all the way out, then you know your coils/distributor is getting plenty of voltage so it is good, and is most likely your spark plugs. If you barely get any spark, especially when the tips are almost touching then you're not getting enough voltage for some reason, which indicates a bad distributor/coil packs, or bad wiring somewhere between the coil packs/spark plug wires and the positive battery terminal.This tool is an excellent little diagnostic tool to have, and I recommend that every mechanic should own one! This is a great tool to help fix misfires and other ignition issues!

I needed it for home standby generators and they just don't produce enough spark. I had to have it wound almost all the way down to get anything at all. Works great on my car, but that's not what I really needed it for.

Good quality tool.

Works great

The item was as indicated, and packaged in order to prevent damage. I have not used it yet, but was ordered because it can show the spark.

I have a 1966 mustang I6 that this came in handy for checking the quality of the spark. With it set to the expected range by screwing in or out the pointer it was clear that I was getting a weak spark. After swapping the points, condenser and coil then retesting, a nice large blue spark was clearly visible while sitting in the car and turning the engine over.

Number 1 reason to buy this over the glowing type tester is you can accurately measure the strength of the spark. I had a weak ignition coil but it was firing. This tool tells me my spark can only arc half the gap of a normal output. Saving me lots of time and money, since I can focus on improving the spark quality. Before using this tool, I thought I had bad gas, dirty carb, worn rings even sheared timing gear. Solved my chipper no start problem. It wasn't clear in the instruction that you do not test it in-line with a spark plug - it tests by acting like an adjustable spark plug outside of the combustion cylinder.