Fuel Level Gauges Autometer How They Work How To Install Tutorial Instructions Ohms Wiring


Year after year one of the most common topics
we deal with on the Auto Meter tech line is fuel level gauges. While one of the simplest
gauges we make, there are a number of variables that have the potential to trip you up if
you’re unprepared. We decided to take a road trip to put together some information [inaudible
00:00:15] out. Hopefully we can help you to get your fuel level gauge installed correctly
the first time or sort out one that isn’t functioning the way you want it to. Now for the past 100 years or so, the basic
concept of the fuel level gauge and sender hasn’t changed. The gauge is in essence an
O meter with an E and an F rather than numbers to indicate resistance. Typically the sender
has a flow of some sort attached to a rheostat that varies resistance depending on the position
of the flow. These can be on an arm or sometimes in a tube. Some are capacitive and have no
moving parts at all. Now regardless of the type, their function remains exactly the same.
Auto Meter makes gauges in a number of different resistance ranges as well as [inaudible 00:00:59]
units, should the range of your sender not be covered. We got this old Chevy here to use as a test
bed. Everything is easily accessible and out in the open on this truck, which makes it
the perfect demonstration vehicle. The first step in getting your fuel level gauge working
is to determine the resistance range of your sending unit. We need to know what the sender
reads at full and at empty to select the proper gauge. Because our Chevy has the sender right
behind the seats, we decided the easiest way to do this was to simply remove it and perform
a bench test. After disconnecting the fuel line from the pickup tube, we removed the
retainer ring and then very carefully pull the sender free from the tank. We don’t want
to bend the arm during removal as that’s a whole nother set of issues we don’t need.
Having a shop towel close by is a great idea as we don’t want to drip fuel all over the
interior. The resistance ranges Auto Meter has available: our zero to 90 ohm for mid
60s through mid 90s G-Ms, zero to 30 for older G-Ms, 73 to 10 for older Fords and Chryslers,
16 to 158 for more modern Fords and 240 to 33, which is sort of a universal after market
branch. Once everything’s out, you’ll want to put a towel over the hole to keep the cabin
from filling up with fumes. With the sender on the bench, we then hook the positive lead
of our own meter to the signal terminal and ground out the negative. We slowly move the
arm up to full and observe the results. Now you’ll almost never get one that reads exactly
what it should, but this particular unit is a nearly perfect zero to 90 ohms. Based on
this information, we select a corresponding Auto Meter gauge. I’m partial of the American
Muscle series, so that’s what we’ll be using. We put together the wiring by crimping quarter
inch spade connectors to the ends. There are a number of after market wiring harness manufacturers
that also offer one piece connectors for Auto Meter gauges if you prefer to go that route.
Now when running gauge wires, the one place you don’t want to take a shortcut is the grounds.
I fix more malfunctioning gauges by moving the ground wire than any other single step.
Take the extra couple of minutes and ground the gauge directly to the engine. With the
wiring out of the way, it’s time to reinstall the sending unit into the tank. Just reverse
the removal steps and you’re in business. Now in many cases, we’ll also add an auxiliary
ground wire to the body of the fuel level sender. An insufficiently grounded sender
can cause problems with gauge accuracy. We tested this vehicle beforehand and determined
this step wasn’t necessary, but if you aren’t sure whether or not your take and sender are
properly grounded, it’s always best to air on the side of caution. So let’s look at some common symptoms on fuel
level gauges. A poor connection with the signal wire can cause the gauge to read higher than
it should or peg out completely as we see here. A bad ground for the sending unit can
cause the exact same problem. A poor gauge ground can cause it to read lower than it
should or not come off the [inaudible 00:04:07]. This holds true for all gauges where higher
resistance means a higher reading such as the G-M and newer Fords. On gauges where a
lower resistance level means a higher reading like the universal after market and the early
Ford and Chrysler, the steps are reversed. Well I hope this has helped to shed some light
on fuel level gauges. As always, thank you for choosing Auto Meter for your winning ride.