Ambient lighting wiring question (basic EE)

Hi team!

I wanted to give my prius v some ambient lighting and I decided I wanted to do it myself. And for the most part I've been able to get really good results for around 20 dollars and a little bit of time.
I bought a 16ft rgb 5050 led string, cut it into 6 strip and wired it continuously through the car and under the seats. I hooked it up to an add a fuse and placed it into an empty slot in the fuse box under the dash.

Here's my issue & question.

The out of the rgb lights the green consistsantly stays on. This means the red color doesn't come through and the blue is more light blue than anything. Even when I turn the power off of the strip (still receiving power from the car) the green stays on.

I have read that sometimes this can be due to too much power reaching the leds.

1.Am I using the add a fuse correctly? Even though it's being inserted into a blank slot do I still need two fuses in the add a fuse? It doesn't work with just 1 fuse in there. In order for it to work there is a 3 amp fuse and a 5 amp fuse does that mean I'm giving it 8 amps?
2. If I'm using a 3amp fuse, does it matter which empty slot I put it in? Isn't the purpose of it to only let 3 amps through? I didn't see any fuses in there that were under 7.5 any suggestions on which slot is the best for an accessory like this?
3. Should I use a stepdown converter to get less voltage?


Some info
The lights work perfectly when I plug it in to a wall wart just not when getting power from the car/fuse box.
I have used many different controller boxed for the led strip all with the same result.
The controller box says input voltage DC12V output current 6 amps max
I don't want to get power from the cigarette lighter (prefer a cleaner look)

Thanks everyone for the help!

 

Thanks for the response!
These strips are pretty cheap so that's always a possibility.

It is plugged into a slot that only receives power when the car is on.

Apparently a wall wart is what you think it is-AC plug that plugs into a wall. I must have picked that up from a brittish messageboard.

Thanks for the info about the add a fuse I think I'll switch around the fuses so the lower amperage is the limiter. I'll update if that worked!
Thanks again