Cargo lamp fuse blowing

[GOMD]

Having an issue on my 2017 Silverado LT, that I added towing mirrors to last year, all factory chevy parts, including new harnesses, with 0 issues, until recently.

 

Last night, went to use the 3rd brake light cargo light, by turning on the switch on at bottom of dash. Cargo light, and mirror lights came on for about 10 seconds, before all going out. Changed the fuse today, and when turned on, they blew right out again.

 

Only other "mods" I have, are a set of footwell lights, wired into the accessory power in drivers side fuse panel. Any reccomendations as to how to diagnose my issue? I guess there may be a short somewhere, in either the mirror wiring or cargo light wiring? Or maybe some water entered into 3rd brake light, which I have seen others complain about the seal in the past. 

 

Thanks in advance.