Installing Fused Switch in Dash

[John_M]

Next week I'll be helping a "mechanically challenged" friend install a lighted toggle switch in the center of his dash panel somewhere below the radio (he thinks). A 12ga wire from the switch will be run back to his factory installed trailer hitch. He and his 2003, 4X4, 47re/SO, SRW are out of town and I had only a few minutes this week to look at the dash and under the hood for connectors, etc. I have not yet seen the toggle switch but I would imagine it has a grounding connector on it. This toggle switch will be constantly "hot", much like a direct battery connection but I don't want to connect to the battery. There is a female brass threaded receptacle in the fuse box within the engine compartment and I could use this for power but then would have to find the threaded stud (probably metric) to use for the connection and would also have to install an "in-line" fuse holder.
There is a 12V receptacle in the lower left center of his dash below the radio almost at floor level. This receptacle appears to be unswitched, fused (20A?) and always hot so I would like to splice into it for power. I have all the necessary quality wiring, connectors, crimpers and solder to do the work properly but am unfamiliar with the Dodge setup. I am more concerned about doing the job right than doing it fast-but I don't want to spend all day on it. Here are my four questions:
1) What is the "trick" to removing that receptacle from the lower part of the dash panel?
2) Where is the best place to run one or two 12ga. wires through the firewall?
3) Is there a convenient common ground connection under the dash or should I just look for a metal chassis connection and self-thread a screw w/star washer through the sheet metal?
4) I should disconnect the battery to do this work because I'll be splicing into and working with a constantly "hot" wire. However, if I am very careful, I can probably do the work without causing a short circuit. If I do disconnect the battery must I reset codes or do some other work with which I am unfamiliar to get his electrical system working properly again? Should I leave the battery connected or disconnect-what do you recommend?

Some of you board members have already done a lot of this kind of work on your 2003 Dodge trucks. I feel much more comfortable using your experiences rather than "winging it" on my own and discovering later-on that there was a better way to do it.

Best Wishes,

John_M