C4 and C9 bulb strings are parallel, but mini lights with a 3-wire cord
are generally series. If you look at the rating of each bulb, they run
in the 2 to 6 volt range so series is used to divide up the 120v amongst
them. To give you added length, they will divide the set into 2 or 3
sections, hence the extra wire(s). A common set size has 100 lights
divided into 2 sections of 50 with each bulb rated for 2.5v to give you
the voltage drop on each bulb that 'uses up' the available 120v. If you
have self-shunting bulbs, each time one burns out, the set gets a little
brighter... at least up to a point. Self-shunting bulbs are becoming
very common and could be mistaken for a parallel setup since the whole
string doesn't go out when a single bulb fails. If you remove the bulb,
the string will go out though. The real problem with these mini light
sets is when every manufacturer uses different sized bulb holders and
different voltage ranges. You can never find the right replacement
bulbs again. :| -Scott

Ismaeel Abdur-Rasheed wrote:

Ismaeel Abdur-Rasheed wrote: