I have a few strings of tree light that won't work. How can I fix that and differentiate between blown fuse or blown bulb in the string.

Since replacing the fuse first would be the easiest thing to do, I would try that first. As far as one bulb causing the problem, sometimes you have to go through and wiggle each of the bulbs that are not lit individually to find the one that is causing the problem. That's how I do it. Perhaps others will also come along with their ideas.

They make a light tool, walmart had them, that finds the short ( or bad bulb) in the lights,
As for as the fuse, you open the little slide and check the fuses first

I didn't know that about the light tool, Fr_Chuck. Thanks for the information!

Those strings of a jillion little bulbs wired in series have dampened my Christmas spirit for many years. If anybody suggests it was stupid of me to buy some made in China ones at Big Lots, well... It was a fight every year to get them to light. It was easier after I bought a voltage detector.

From Labman's hoard of old AMHD answers:

To do simple checks like this you do need some tools. A test light, a meter, or a voltage detector might be the best place to start with. I came across the niftiest gadget for trouble shooting, a voltage detector. They work through the insulation of wires. There are several brands. I have a GB Instruments GVD-505A, less than $15 at Home Depot. Touch it to a hot wire, and the end glows red. Find the doodad that lights it on one side, and not the other, and you have the culprit. You do not have to open up housings and expose electrical contacts. You are looking at where your hand is, not where the meter is. Most people are capable of doing repairs and will get it going and not get hurt if they use a little sense. The voltage detector makes it even easier.

With it, I was able to get the 2 outdoor angel light sculptures going in about an hour. Last year, I trashed them and bought a molded plastic nativity scene that had a single light bulb in each figure. Likely took less than 10 minutes to haul them out of the attic, set them up and plug them in. They all 3 immediately lit up. With CFL's, I have calculated that if I leave them on 24/30 for the season, I will use 3 KWH. I will also be saying Merry Christmas through clenched teeth less this year.

Funny thing. Of the 6 strings of lights I bought from Sears in the mid 70's, 5 still work. With the smaller trees my wife and I buy now, I only use 4 strings.

I think the hot item now is LED lights.

Well I sold off all of mine 1000's of them with riegn deer, santa suits and more a couple of months ago when I down sized to my new condo life.

I used to have over 10,000 lights plus several artificial trees and tons of other things. I normally picked up about 10 to 15 new light sets each year ( after season for the next) and threw out 4 or 5 that had become trouble.

I picked up that testing tool about 3 years ago, sames time, but still have to test to find problem. Also if you have big time lights use card board or plastic holders and wind up the lights each year ( even mark them as to where they go) then store them in air and water and moisture tight plastic tubs for the season.

This is my first year in 30 years I have not had a outside light

Yea , China, I hope we all like Chinese food.

Funny, I saw an article today, the Chinese shopper are looking for foreign stuff in their stores. They don't trust their own junk.

I warn you, keep an eye on them.

This site has a bulb and fuse tester -- also checks for power along the string

\Howstuffworks "How do proximity-type Christmas-light testers work?"

This site has some good information on xmas lights

Howstuffworks "How Christmas Lights Work"

I know these lights are cheap but with a little care you will get your moneys worth

I will never buy another string of them.

Why do you think the price of oil is around $100 a barrel? It's not OPEC doing it because they can, it's because China is become very industrialized very fast. Their demand for oil is skyrocketing and driving prices through the roof. And it's just starting...

We just opened brand new boxes of Christmas lights and only half of the strings work. I swear, they make them like that on purpose.