Setting up a resistive fuel-level sender
A classic fuel-level sender is a variable resistor to ground — the float arm changes its resistance as the level moves. The Expander reads it directly: the fuel-level channels have on-board software-selectable pull-ups, so a 2-wire resistive sender just connects to the channel and you pick the range in the dash. No external resistor, no harness tricks — the same on both the Standard and the Pro.
Why it just works
The Expander's analog inputs measure a voltage. A resistive sender only changes resistance, so on its own it gives the input nothing to read — it needs a pull-up to a reference to form a divider. On the Expander that pull-up is built in on the fuel-level channels (a software-selectable network), so the board turns the sender's resistance into a clean, ratiometric voltage for its 16-bit ADC. You choose the range to match your sender and calibrate the ends — that's the whole job.
Wiring the sender
Pick the channel
Fuel level uses the AN3 / AN4 analog channels (the two fuel-level inputs) — find them on the analog connector by the board's silkscreen channel labels.
Connect two wires
Sender signal wire → the channel's signal pin. Sender ground → the channel's return / ground pin. If your sender grounds through the tank flange (single-wire), it returns via chassis — workable, but a dedicated return to the channel ground reads cleaner.
Secure and protect
Crimp and heat-shrink, keep the run away from injector and ignition wiring, and loom it in. That's the hardware done — nothing else to add.
Set it up on the dash
Everything else is in the Helm Commander configuration screens — no scan tool:
- Assign the channel (fuel level 1 / 2) to fuel level.
- Turn on the pull-up and pick the range to match your sender — a ~90 Ω range suits GM / Nissan senders, a ~240 Ω range suits Ford / European senders. If the reading barely moves between empty and full, switch to the other range.
- Calibrate the ends: set the reading with the tank empty and again full (or move the float by hand on the bench). The dash maps the voltage curve to a level from those two points.
- Watch the live value track as the float moves — it should be smooth, with no jumps.
Troubleshooting
- Reading pinned at full scale and dead — the pull-up is off, or the sender/return is open. Enable the pull-up for the channel and check the two wires.
- Reading pinned near zero — signal shorted to ground, or a shorted sender. Meter the sender across its two terminals.
- Tiny swing between empty and full — wrong range for this sender. Switch between the ~90 Ω and ~240 Ω ranges.
- Jumpy / noisy level — poor sender ground; run its return to the channel ground rather than a random chassis point.