Common install technique or stupidity?

I have a question about the installation that people had a shop do or did yourself...
Got my new Leer home (show me your cap post 3505) and tried to use the light. The sales guy said that I need to turn my park lights on in order to use the interior light. I didn't think much of this instruction as I was running to visit a friend who just got out of the hospital before her nurse visited her. So last night I tried every incarnation of parking, driving and break light I could possibly do. No dice, interior light wouldn't turn on. I figured it was not operating correctly if at all so I went back today. Had a frustrating conversation with the installer who basically wiggled the badly zip tied loom near the fusebox they mounted and made it work. I asked him exactly how he wired it. Basically said T taps on brake light for the top break light, T tap off the running light for interior light and T tap off a ground for common ground. I was shocked. They T tap off a 20AWG wire to a box they fuse to 5A? How does that make any sense, the wire will burn up the harness before it blows the fuse. Needless to say I was concerned and asked him to re do it correctly. He refused, said they had been doing it this way for 10 years without issue. Not much I can do about that. So I got it home and ran a 14AWG wire (and a 10AWG as a spare in the same loom) from a new fuse off the battery (temporary as I want to put in a sub panel for cool accessories) I soldered the new positive to the interior light input to the box they installed and relocated the common negative to a screw in the tail light. I took photos of the hack master original install, complete with 5ft of wire electrical taped and stuffed in the tail light. I will post photos later and email the shop managers. I am kind of livid about how stupid their practice seems, let alone the attention to detail.
Is this common practice? I can't see it being anywhere close to a good idea.

 

i wired mine i bought my cap used for interior lights i ran wire from battery to back with 20 amp fuse by battery the light inside cap has a switch to turn it on and off and for 3rd brake light i tapped into wire for trailer connector under the truck.

 

The wiring is good for 11a, light isn't going to pull 5a by itself. It's not the best, by far, way to do it. But it should work.