I am a neat freak and always hiding my wires. But I have messed up twice already and dont want to do it again.
I am trying to hard wire my Grarmin GPS so i do not have wires running across my dashboard.
The very first time i took the Garmin car charger and cut off the part where u plug in the cigeratte lighter. Their were two wires. One is negative and the other is positive. The negative wires is surrounding the positve wire. So i thought it was going to be simple. Connect the positive into the fuse box and ground the negative. I was wrong, right when i plugged in the navi, it fried up. The smell of burnt wires and chips was strong. I blew my navi.
I then contacted garmin and they sent me a new one.
This time I put a fuse between my gps and the fuse box. I got an inline fuse with a 30 amp fuse. Connected the GPS and it fried again!!!
Was a 30 amp fuse too much?? should i get a smaller one like 10?
i contacted garmin again, they sent me another one. Just got it back today.

 

I don't think you are wiring this right at all...

Is it a dash top navi or a double din navi like a head unit?

If you give it power and a ground, it will only draw what it needs, fused or not. One of the wire you're connecting isn't correct.

 

It is a regular Garmin Nuvi 350. not a headunite.
I did the samething with my passport escort x50 but instead i bought the hardwire kit from bestbuy. Garmin does not have a hardwire kit. My radar detector has the exact same setup. Fuse box to inline fuse to radar detector. Negative to ground. And it works fine. My radar detector is hidden at the top of the windshield near the driver side piller. I am trying to get my navi right under that.

 

I'm in a rush to leave so I didn't read your whole post, and only have time for a short response. Be 100% that the cigarette plug is not an inverter, your GPS may run off less than 14v. If there is no label on the plug, plug it in and measure the voltage, if it is less than 13v with the engine running, the GPS requires a lower voltage. So you will have to wire that plug to the ACC line then you can power your GPS, that is if you didn't fry it hitting it with 12v.