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The FSM indicates that a bulb grounded through the sending unit with 12V should FLASH... Which doesn't make a lot of sense if it's resistance based.

The test light should flash, because the sender does not continuously ground the circuit... It pulses the grounding at different rates, thus the faster the pulse, the higher the temp on the gauge coil. This results in a higher reading on the gauge.

Shorting the circuit causes too high of a temp on the coil, and permanently bends the coil, causing the needle to show very low pressure at max, and nothing below that.

"A young man who does not have what it takes to perform military service is not likely to have what it takes to make a living." - John F. Kennedy

Proud owner of an 88 Montero (with a blown engine).