What brand of gauge will you use?
These Stewart Warner brand fuel senders are compatible with all Stewart Warner and Classic Instruments fuel gauges.
How deep is your tank?
Measure the depth of your tank where the fuel sender arm will be located. Choose the sender with an operating range which includes that dimension.
Right or Left-swing arm?
Most fuel gauge senders attach with a 5-screw pattern. Two of these screws are farther apart than the other three. Position yourself such that the 2 wider-spaced holes are closest to your chest; a right side sender will have the arm (or "float") extending to your right, and a left side sender will have the arm extending to your left. This only matters when replacing an existing sender. A first-time installation can use either one, just drill the mounting holes accordingly.
LH/RH Swing Guide (Link)
The OEMs used several different resistance ranges for fuel level indication over the years. However, some of the aftermarket gauge manufacturers follow the common Stewart Warner values (240 ohm empty, 33 ohm full). The gauges and senders that we carry (385 & 391) use these standard Stewart Warner values.
Ohms Chart (Link)