This is one of those projects that some people will simply read and think, "Why?". That's okay, I get it. Who needs a fuel gauge? Well, I do. I'm OCD that way. So, the first question I had to answer was, "Can it be done?" That answer is yes.
After some lengthy research, I determined that our OEM fuel level sensor is exactly the same part number as the same model year(s) Sprint ST, which has an OEM fuel gauge. That means that it is fully capable of providing a correct signal for a gauge, even though our bikes only have a low fuel warning light.
I originally purchased a used gauge from a Sprint ST for $12 USD for testing. The gauge was too large for practical mounting capability, and had zero "bling" factor. DEcosse has covered the specs on the sender itself in his own post, so I won't get into that here. For the purposes of this post, however, you must know that the resistance ranges for our senders is odd in that it isn't common to anything. The range is 13 ohms full, to 91 ohms empty.
There are no aftermarket gauges that are programmed for that specific range. Therefore, I chose a fully programmable gauge for the job: Auto Meter Pro-Cycle 2-1/16 fuel gauge, p/n 19609. I also bought the matching voltmeter, p/n 19692. The way I wanted to mount them gave symmetry to the look, and I've also had R/R issues in the past, so the voltmeter was a must.
Before I get into the retrofit, I will add that my configuration safely disables the low fuel light. There is a potential to have both the gauge and the light both work as there is a gauge output pin on the ECU. Unfortunately, there is no wire in that hole and no practical way to install one. I chose to bypass the light circuit.
- Auto Meter 2 1/16 in. Pro-Cycle Fuel Level Gauge - 19609
- Auto Meter 2121 Carbon Fiber Gauge Mounting Cup x2
- 47 ohm resistor (Radio Shack)
I also installed the voltmeter, but that's a straightforward install and not discussed here. The gauges are blue LED backlit, so I also converted my instrument cluster to blue LED with excellent results.
I chose the cockpit sub-frame as my mounting point. The brackets came with the mounting cups:
After securely mounting both gauges and ensuring that the setup would clear the headlamp assembly, handlebars, and everything else, I wired in the gauges. I tapped directly into the main harness for my ground, key on gauge power 12V, and into the "park" light circuit for the backlight:
Note that all taps were made with clean, soldered connections and sealed afterwards. Any electrical mods done on a bike need to withstand the elements. Good, permanent connections should always be soldered, period.
Next, I needed to modify the OEM sender wiring to "fool" the ECU into keeping the low fuel light off. This must be done properly in order to keep both the low fuel light and the check engine light off. This was accomplished with the 22-ohm resistor. The sender then bypasses the ECU to provide a clean signal to my gauge:
Lastly, I followed the instructions to calibrate the gauge to the "odd" resistance range. This is done by placing the gauge into a programming mode with the tank empty (I called "empty" 1/2 US gallon), and after registering the "empty" value, filling the tank and then registering the "full" value. Now the gauge reads the full range, and fairly accurately. Because of the tank/sender configuration, the gauge remains on "full" for quite a long time. Then it begins to read accurately thereafter, all the way to "empty".
Here's the finished product (image doesn't do it justice; the blue is absolutely gorgeous):
I'm very satisfied with the results. It was an expensive project; each gauge was over $160 USD, and the cups were $55 ea. It was fun to accomplish, and I hadn't read of anyone trying it before. Hopefully you find this useful, if not merely entertaining.