I am a complete beginner when it comes to electrical wiring.
Could somebody shed some light on how I can achieve what has been described in the attachment.
I appreciate your time greatly and I would be happy to Paypal you the cost of a beer.
Try a read here with all my experience (in Italian):
(1) Connect (+) side of power supply to all 4 com terminals of the relays and center of 12V power plug.
(2) Connect (-) side of the power supply to the outside shell of the 12V power plug.
(3.) For the lights connect the (+) terminal to a relay N.O. and (-) terminal to (-) side of the power supply.
(4.) For the fans connect red wire of first fan to a relay N.O. Connect the black wire of the first fan to the red wire of the second fan. Connect the black wire of the second fan to (-) side of the power supply.
Use a meter and be sure of your polarity as reversing (+) and (-) will cause damage. Note that connecting 12V fans in series will result in lower speeds. With identical fans each will only be running on 6 volts. You could connect them in parallel (red to red to relay N.O. and black to black to power supply (-)) to make them run at full speed and load.
Once again, watch your polarity! You are basically feeding the (+) side of each device through the relay switches and tying all the (-) sides to the (-) side of the power supply. Use wire preferably colored red(+) and black(-). Speaker wire or automotive wire is suitable for this low voltage use.
You can carefully splice into the power supply lead about 6 inches behind the plug as one method. Solder and insulate all connections.
No need. Good luck with it.