LED Brightness on Rev. C?

So I'm blinking an LED on pins 7-12, and they are EXTREMELY dim - like stare at the contact point and see a spot of light. When I test on pin 13, it's much brighter. I then tried to blink just 1 LED on pin 12. I've tried it on two different breadboards with the same result. I've tried two different Rev.C boards with the same result, and an earlier version of the board which produces the expected brightness (read full brightness). Also tried with power adapter instead of USB power to no effect.

void setup() {}      

void loop() {
digitalWrite(12,HIGH);
delay(1000);
digitalWrite(12,LOW);
delay(1000);
}

Pretty basic. Very confusing. Is there something I'm over looking? Is there something to set the level of the output?

hi

did you use a resistor in series with the LED? Pin 13 has one built in. Directly connecting an LED to a pin will overload the pin and result in things like very dim leds...

No. It wasn't that - I used resistors. I figured it out. It was that I hadn't set the pins to OUTPUT with pinMode. But thanks for the thought.