GPS models with a cigarette lighter plug almost always have a 12V-5V converter in the plug. Most don't do well cutting off the plug. Check with Garmin. A fuse block is a good idea if several devices are planned. The Eastern Beaver site has good info as does .: Distribution Block / Powered Relay | Canyon Chasers Motorcycle Sport Touring :.
The latter site has clickable pictures for larger views.
The latter site has clickable pictures for larger views.