Originally Posted by Sky
Don't mean to hijack this thread, but guess I am. What do you mean
"with resistor built in"? I just ordered a 12v green led for a water-pump-ON
indicator. I was planning to hook it in parallel where the 12v power line enters
the pump. Whats this resistor stuff?
LEDs are available with or without a built-in dropping resistor. If you hook one without a resistor directly to 12V, you get exactly one very bright, but very, very short burst of light. The Radio Shack LEDs have the resistor built in so that you can tie them in to any 12V circuit without any other component required.
I have some LEDs without resistors as telltales for other switches in my trailer. For each of these LEDs, I used a resistor from my parts box to limit the current.