Coil test, how long?

[Ian in Mississauga]

I read about a coil test that involves getting a bright blue spark from the secondary wire, then leaving the key on and points closed and doing it again. How long do I wait between the two observations?

 

[Bob Bidonde]

It takes milliseconds for the coil to saturate, so all the time you need is a blink of an eye.

 

[alexiskai]

I think the OP was referring to a technique of warming up the coil by allowing current to flow through that circuit for several minutes, and then testing the spark again. I've heard this mentioned but honestly I don't think it tells you a whole lot. Even a failing coil can usually manage one spark when it's hot – and meanwhile you could be degrading the points by leaving that circuit on for several minutes.