Many already do this but i thought id throw up a quick guide anyway
Warning:
Heatshrink your RCA plugs first. RCA's have an exposed conductor, if it touches another 12v Ground point (Metal mount/Tripod) it will trip the fuse.
Materials:
12v PWM dimmer switch - $3.18
12v Cigarette plug w/ bare ends (5A fused)- $2.95
RCA chassis socket – 95c each
Hook up wire – Free (scavenge around)
Tools needed:
-Screwdriver
-Soldering iron/solder
-Drill
-6mm drill bit
I think the photo is self explanatory. The RCA socket is drilled into the box then soldered to the PCB's underside terminals.
I only put one RCA socket as i use a splitter. You can mount as much RCA sockets you can fit, up to 8A worth of straps. The external output connectors (bare wire) are left free if you want to double purpose this controller for LEDs and such.
You can rip out the red LED from the cig plug and solder it on like the RCA sockets. The box is semi-transparent so it will glow redder the higher the PWM setting.