I'm trying to figure out how to control the color in the LED 5050 RGB strips--how are the 4 contact points usually mapped (my strip does not indicate). I'd also like to ratchet down the brightness--the strip currently runs on 12V/5 amps. To ratchet down the brightness, is that a reduction of voltage or amperage; how far can I ratchet down and still expect the LED strip to function; and how best to ratchet down?
The 4 conctact points are usually R/G/B anode/cathode and the 4th is common cathode/anode. AFAIK both variations exist.
To control the brightness, the normal way is to use PWM - switch on the required power for a short period of time, switch it off. Do this at a high frequency.
By altering the time it is on/off, you can control the brightness.
Simple rgb led strips with four conductors come in both Common Anode (V+) or Common Cathode (Ground) options, with the other three conductors being the individual color pins. They also come in 12V nominal and 24v versions.
You can adjust brightness with a PWM controller, but a simple method for a constant brightness reduction is under volting the led strip. The 12v nominal strip works from 10 to 14 volts. The lower you go the less bright. 10 volts is about the minimum that you can go like this.