bed lights

[gave20]

I've done some searches and have read through the posts on wiring additional bed lights to the cargo light circuit. Most of the posts talk about using a relay to make the series work. Maybe I don't understand or am confused but I found the two wires the run the cargo light; why can't I either splice into them at the mid bec or tie the cargo light wire and the new bed light wire together into the metripack pins at the mid bec cargo light posts? Will this overload the circuit? Do I have to add a diode?

 

 

I was thinking of getting the marine rope lights from cabelas.