Replace the tank when it's rusty, leaks, or you're converting to EFI — and if you're going EFI, buy the in-tank pump tank now rather than hanging an external pump that whines and cavitates. A bad sending unit usually means a stuck or fouled float; you can sometimes fix the gauge without dropping the tank, but a rusty tank is a safety issue, not a maintenance item.
The early Bronco's fuel tank sits under the cargo floor (later models) or in the original under-seat location on early trucks, and after 50 years many are rusty inside. Rust flakes clog the pickup and EFI injectors, and a pinholed tank is a fire hazard you don't drive on. The sending unit — the float-and-resistor assembly that drives your fuel gauge — fails separately and is the usual reason the gauge reads wrong.
If you're staying carbureted and the tank is sound, a new sending unit fixes a dead gauge. If the tank is rusty, or you're converting to EFI, replace the tank — and for EFI, get a tank built for an in-tank pump so the pump runs cool, quiet, and primed.
Decide your fuel system first. A carbureted truck uses a mechanical or low-pressure electric pump and a basic sending unit. An EFI conversion needs 40–60 psi from a high-pressure pump, and the right way to feed it is an in-tank pump module that sits submerged in fuel — it stays cool, doesn't cavitate on hills or off-camber, and is quieter than an external pump. Tanks built for the early Bronco with an in-tank pump and matched sending unit make this a bolt-in.
For the sending unit, match the ohm range to your gauge. The factory early Bronco gauge expects a specific resistance sweep; an EFI module's sending unit must match it or the gauge reads wrong even with a full tank.
Work outside or in a well-ventilated space with a fire extinguisher in reach, and disconnect the battery. Drain the tank as low as possible — run it down before the job. Support the tank, disconnect the filler, vent, fuel lines, and sending-unit wiring, then lower it. Transfer or install the sending unit and pump module, using a new lock ring gasket. Reinstall, reconnect lines and wiring, and pressurize the system to check for leaks before the first start.
Calibrate or verify the gauge: with a known fuel level, confirm the gauge tracks. Mismatched ohm ranges are the usual reason a fresh sending unit still reads wrong.
Fuel handling is a safety issue. Vapor is the hazard, not the liquid — no sparks, no smoking, ventilate, and keep an extinguisher within reach. Don't drain a tank near a water heater or any pilot light.
An external high-pressure pump feeding EFI is the common shortcut and the common headache: it whines, runs hot, and can lose prime on a steep climb or off-camber, stalling the engine at the worst time. An in-tank pump avoids all of it.
Ohm-range mismatch between sending unit and gauge is the quiet failure — the tank's fine, the gauge lies. Confirm the range before you button it up.
A replacement carbureted tank with sending unit runs $200–320. An EFI-ready tank with in-tank pump module runs $350–550. A fuel tank skid is $100–150 and matters once a lift drops the tank below the frame. Total for an EFI-ready setup with skid is $450–700.
You probably don't need to drop the tank for a gauge problem if the tank is sound — test the sending unit and wiring first. But if there's rust inside, replace it; a clean fuel supply protects everything downstream, and on EFI a dirty tank kills injectors.
| Part | Vendor | Est. price |
|---|---|---|
| Replacement fuel tank (17.5 gal, early Bronco) | Tom's Offroad / LMC | ~$200 |
| EFI-ready in-tank pump + sending unit module | Tanks Inc. / Aeromotive | ~$350 |
| Fuel tank skid plate | Various EB fab | ~$120 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.