flyerrich;

While I have found its possible to briefly test LEDs with a 3v battery, and no resistor, I never install an LED in anything without a resistor in series with the LED. The reason the resistor is needed is to limit the amount of current that flows through the LED.
Granted, the amount of current, and therefore the value of resistor needed, will vary with the amount of voltage applied, but an LED without a resistor is very likely to burn out, even on quite low voltage, because of the current passing through the LED, rather than voltage.
I suggest you put a 680 -1000 ohm resistor in series with the LED. If you are sticking to 3 volts, you can experiment with lower value resistors. However as soon as the LED gets brighter don't drop the resistance further. You can increase the resistor value to dim the LED a little bit, or decrease the resistance a small amount for the LED to run a little brighter. We don't really have as much brightness control with LEDs as with incandescent bulbs.

Good Luck & Have Fun;

Traction Fan 😊

 

Also check to see how much voltage the power supply is actually putting out. I checked some "wall wart" power supplies I have and found some to put out way more than their labeled output.

 

Well guys much to my surprise my LED"s that flashed and went out was because of a bad connection where I had them attached to the light buss I made up. Only one light was attached to a barn the other one was not mounted to a bldg. yet. I removed the one from the bldg. and replaced it. This one worked. I then checked the two that had flashed and found both connections loose. I had not soldered them yet. Now I attached the leads to a distribution board that I also purchased on Ebay from the same seller. This has a pot that allows you to adjust the light brightness. As I said the input is 3 volts DC, which the seller said I didn"t need any resistors as long as I used 3 volts. More than that I would have to install resistors. I am thinking if I put resistors on the led's using 3 volts ,maybe they won't light. Your opinions please.

 

As traction fan said, its best to put resistors on each LED to help limit current. Sometimes a Power Supply sends a little "extra" voltage at the start and the resistor is great protection. Sounds like you have a way of testing for what size resistor you need by using one LED and that Pot to see what brightness you want and at what point the LED shuts down. Adjust the pot then disconnect the Pot from the circuit and using an Ohm meter, measure the resistance. Because the LED's are current devices, using a resistor per LED will result is less messing around trying to adjust the single Pot for the varying load of LED's.