inline spark plug tester?

[MarkAllan]

I bought a in line spark plug tester and I want to confirm that it is working? if I touch one side to pos and the other to neg on a 12v battery should the light come on?

[Dave Neptune]

Most of the testers do not have a light. What you see is the spark jumping across a gap, just like laying the spark plug on the block of the engine and seeing the spark when cranking. The tester just has a bigger gap.

Dave Neptune

[Al Schober]

That confirms my thoughts. Back in my outboard days, my spark tester was a piece of wood with two wires stapled to it to make a 5/16 gap. One lead to the coil wire, the other lead to either the block or the cap on the spark plug. With the lead to the block, you're verifying good spark. With the lead to the spark plug, no spark says bad plug.

[MarkAllan]

this one has a light buld

I bought this at Canadian tire for $10.00 it is something that you place between the spark plug wire and spark plug. If the light turns on you are getting spart to the plug. Anyways I tried it on cylinders 1 and 4 and it shows no light. I tried taking the plug out of #1 and holding it against the engine block I had a friend turn the engine over and I got NO spark at the plug. I ran out of time so now when I get back to the boat I going to investigate further.

So question does the spark plug work off of 12 volts ?? I am questioning if this tester is working so I tried putting it to my battery and the light buld does not light up? But maybe the bulb requires a higher voltage to work?? does not the coil ramp up the voltage to the plugs???

[Dave Neptune]

The spark comes from the coil and is anywhere from 25,000 volts or much higher, however there is very little amperage.
If your seeing no spark and the engine does not start you may have a dead coil. Coils often die if the key is left on for any length of time. Check to see if you are getting 12v at the positive side of the coil. Also check to be sure the points are opening and closing.
My first guess is a dead coil, second is no voltage and finally trouble with the points. If you have an EI it is probably the coil if it is getting 12v.
If you are getting no voltage at the coil check the key switch.

Dave Neptune

[MarkAllan]

Is there a fuse to check? first?

[Dave Neptune]

I doubt there is any kind of fuse in the devise, however there should be on the ignition system for the engine.

Dave Neptune

[edwardc]

High voltage testers that employ a lamp are usually using some sort of gas discharge lamp like Neon or Argon. Neon will be a reddish orange color, while Argon will be blue-violet. These lamps just consist of two electrodes inserted into a glass envelope of the appropriate gas at low pressure. In a 12v system, they would just look like an open circuit.