You mean 8.3 Cummins engine? Left hand side of the block, about 1/3 of the way up from the rear of the engine.
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Need to know if it has the Mack or Cummins engine in order to
answer.
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Remove the fuel sending unit from the fuel tank (the process to
do this depends on what your vehicle is), unplug it from the
weatherpack connector, install the new unit, plug it back in.