What does the timing light indicate?

Bingo.

It dicates when a spark occurs, but for the spark to occur the signal must go to the coil..... I'll assume you are using an inductive timing light... it flashes any time high voltage goes through the wire it's clamped around.

I'm using a timing light which connects between the plug and the plug wire with a wire apparatus. Not the inductive Timing light as you mentioned.

Thanks,

William Oliveri wrote in rec.autos.tech

Yes, typically it has a clamp to put around the number one spark plug wire. This clamp picks up the magnetic field of the wire when the plug fires, triggering the light to flash. If the plug is not firing, then the light will not flash. It could be used to determine what cylinder is not firing, or to determine if you are getting spark. Which is perhaps what you were looking for.

same thing, it triggers when there is high voltage going to the plug it's connected to....

Close enough. Different method of achieving the same result. (desired result being "flash when that spark plug fires")

it indicates when there is a high voltage impulse in the ignition wire. that is no guarantee of a spark. there will only be a spark if the spark plug and the iginition wire are good.

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yes

William R. Watt wrote in rec.autos.tech

Of course, the only time you are going to get the impulse is when current flows through the wire from the coil/distributor to whatever is connected at the end. Now, it is possible that if the wires are arcing you will get the impulse but no spark. But that will be apparent from other tests. It is also a remote possibility that the ceramic is cracked on the plug, allowing arcing without a spark inside the combustion chamber, but that is even more rare. As a general rule of thumb, if the timing light is flashing, most likely the plug is sparking.

Another way to find a lost spark is to let the car idle on 3 cylinder for cars with 4 cylinder. A miss will stall it immediately. If you can't idle on

3 cylinders, then it won't work. DO NOT remove the spark PLUG wires. YOU will get GAS on your O2, plugs, damage engine control modules or etc. Removing the fuel injector power source is one way

- but at your own risks. I've done it all of my lifetime.