Use 12v from factory tow wiring for lights in shell?

Has anyone here used the 12volt from the 7 pin plug for overhead light in their shell?
My last shell was originally on my 2007 SR5 without tow package and they ran a separate wire all the way up to the battery for it.
Xfered it to my 2010 with tow package and asked if there was 12v available at the back so I would not have a wire and fuse hanging off my battery teminal and they said no.
Getting a new SnugTop for my 2015 hopefully this week and plan on asking them to do this and if they refuse I'll just have them leave it hanging and I'll figure it out myself.
All 3 times different dealers.
Any reason to not do this?
Thanks.

 

The 12 volt power wire for the trailer plug is an "ignition only" power source. You can tap it, but the lights won't work unless the key is in on or acess position. I just got a snug top and ran power from the battery back for the light (you can also get a battery operated LED interior light on snug tops). The LED vehicle powered light they provide is nice as it works both with the switch, or you can set it to come on when the back lift gate / window is opened. When I ran my power I did it like the post for the bed light install but continued through the cab fire wall to the battery. My tow package has a marine type connection at the battery so I simply put a lug under the existing bolt and installed a weatherproof inline fuse holder at the battery. You can pick up the ground inside the taillight void so you only need to run a single wire from up front.

 

My LEER dealer wired into my parking lights all 3 times that I bought a cap. PITA having to have the parking lights ON, but keeps you from leaving the light ON and killing your battery.

I was not aware that the power at the hitch plug was ACC circuit, I was thinking of doing what you suggested. I guess that changes things.

 

I guess I did not think that thru enough. Makes sense that having a constant hot to a trailer would be a bad idea. When I saw a diagram with a 12V on it I assumed it was from the battery, not.
I'll just let the dealer run a wire to front like all my past shells though I think my last shell the light only was used once in 8 years.
Thanks.