autopage rs 855lcd to turn on cargo lamp

I have an Autopage RS-855LCD installed in my 2003 Dodge Ram. I would like the alarm to turn on the cargo lamp over the bed when it turns on the interior lights (when disarming). Both the cargo lamp and the interior lamps are ground switched. Can someone tell me what wire on the alarm is the dome/supervision output. I need to know how to wire the output to the cargo lamp. Also, would I need to use diodes on the ground wires when I tap into the cargo lamp circuit. Thanks in advance.

Thanks but I don't need to know which wire on the truck is the dome light wire. I need to know which wire from the alarm is the interior illumination output.

It's the White wire (pin 12) on the 20 pin harness for the RS860lcd Here's the install manual for future references Good luck...

opps... forgot to paste... http://www.autopageusa.com/resources/RS855LCD_Install_rv72104.pdf

Thanks. Now I need to find which wire coming from the swithc panel on the dash controls the cargo lamp...any ideas?

I don't see that wire in any of the diagrams I have so this has to be done as a custom install. I would go with enice's suggestion to search for that cargo lamp wire over the bed. When you find it, use a relay and diode isolate it with the dome light wire from the interior light circuit. Wiring should be easy once you find that cargo light wire.. Good luck.