Difference in Engine Wiring Harness (Guages v. Lights)

[4tiresngas]

I bought a new wiring harness for my truck. The underdash harness sstates with guages. So does the front light harness. The Engine harness simply says 69 V8, HEI, Auto. It has the wire for a oil pressure sending unit on it. Do you think they just put it on there so it will work for trucks with or without guages? Is the temperature sending unit wire suppose to be different for guages and warning lights? I 'll post pictures later when the wife gets home and tells me where the USB cable for the camera is. Thanks.