It will flash low when at the 4 gallon mark.

It shows in numerical value, however when i first used mine i was confused by the third character; it always will show lower case "g" for gallons, but it looks like the number 9. For the first 2 gallons of being full it will display "Ful" on the last 4 gallons it will display "low"

As long as your factory sending unit is still providing a signal you will want to use item number
ZX470259X

These are very easy to install . You can find gauge pods on Jcw's site that will allow you to mount them in multiple places

To install you will want to Fuel Gauge
1. Connect red wire from gauge to a switched 12v source (12v switched power source means that there are 12v to the red wire when the ignition switch is on and no voltage when the ignition switch is off)
2. Connect black wire from gauge to a good engine block ground
3. Connect purple wire from gauge to the night time dimming circuit. (The purple wire must be connected to the headlight switch circuit so that there are 12v to the purple wire when the headlight switch is on and no voltage when the headlight switch is off)
4. Connect white wire from gauge to signal wire from fuel sending unit