lx guy:
this is right off the website of autometer:
Will an Auto Meter fuel level gauge work with my existing stock sender?
So, you have decided to replace or install one of our fuel level gauges, or your current system is simply broken. No problem. However, this can be a tricky job, and it will require some thought and research. Fuel level gauges are designed to work with specific sending units that vary with different automobile manufacturers. Auto Meter offers gauge models for use with the existing senders on most cars. Also a sending unit (model 3262) is available to work with certain model Auto Meter fuel level gauges. If you want to use your existing sender and are uncertain about your type of sending unit, or if it even works, an ohm reading will need to be taken when the tank is full and empty. These readings are important, as these are the numbers that we publish with our gauges to assist you in selecting the correct gauge.
Typically, on the top of the sender, there are a minimum of two electrical wires that both have a very important function. One of these wires should be a ground, and it should be attached to either the mounting strap or the frame itself, because it is measuring resistance to ground. For instance, most GM applications have a twist-lock design, there may be no ground wire. The ground is made through the contact of the "twist-lock" mount to the top of the tank. Another example could be that you have a fuel cell, made of plastic or fiberglass. In this case, you have to run a ground wire to the frame to obtain resistance and fuel level readings. A ground wire is needed because the "twist-lock" mounts into plastic/fiberglass and can not conduct a ground to operate the gauge. As you can see the ground is VERY tricky and important, so make sure it is correct.
Now onto the sender wire. This is the wire that sends the signal from the sender, up to your dash and to the gauge. As far as testing goes, you have a couple of options. If you have the tank down or off the vehicle, you can pull the sender and attach your ohmmeter or multimeter to it. Now move the float arm or float up and down, and watch the resistance change. This is how you get your full and empty readings. If you don't have the tank down, you can still test the resistance range. You can check the wires right off the tank that go to the gauge in the dash. You can pull the gauge and test the resistance where wires connected to the gauge. This requires a bit more effort and time, but it is the only way to get a reading. To perform the test, fill the tank with gas and check the ohm reading, then drive it until it is empty or almost empty (as you can see this may not be the most accurate way to get a reading) and take another reading.
Hopefully this gives a little more insight into how to test and correctly connect the fuel level gauges.
Tip: In our instructions you may find it odd that we state to have the tank full when installing a gauge. We want the tank full to show that it goes to full and operates correctly. Otherwise, if the tank is empty and then filled, the needle may only climb a little, and you may think it is not working. Having the tank full is not required, it is more of a check to let you know that the gauge is functioning.
