The shorting bar that closes the low fuel light switch at the bottom of the sender is on the float . If the gauge needle is working correctly, the float is not sitting on the bottom, shorting out the low fuel light switch. So it must be either gunk (carbon?) on the low fuel switch, shorting it out, or fault in the bulb test circuit. I figured how the circuit worked at one time but can't remember details. I think there is a resistor and a diode in the circuit. The resistor lights the bulb at 1/2 brightness.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked