Re: Garmin Quest Hardwiring (electrical question)
Depending on how picky the Garmin is about it's input voltage, this could be a little trickier than you think.
The biggest problem with just using a resistor and a fuse, is that the resistor will just drop the voltage proportionally to the battery voltage, so when the battery is at a lower voltage the GPS will get a lower voltage and vice versa.
Also, as there is a relationship between voltage, resistance and current, (V=IR) you will need to know the GPS's actual current draw to calculate the resistor size for this particular application (this may vary with such things as back light etc.)
A far better solution is to build a little DC-DC voltage regulator, there are heaps of schematics on the net, but this may be beyond your willingness to experiment.
Or find a cheap car charger for a cell phone or something that puts out 5V and cannibalize that.
Or, and this would be my option, pony up the 75 bucks for the kit and have it done tommorrow.
Sorry, long post, kept thinking of different ways to skin this cat.