Engine harness design varies significantly from year to year, but most will contain wiring for the ignition system, starter, heater blower, and temperature/oil pressure sender wires if applicable. Some vehicles used a capillary tube to provide an oil pressure reading, so these will not be included in a wiring harness. On vehicles with ignition points, the circuit feeding the ignition coil was designed with some resistance to extend the life of the ignition point set. Modern electronic ignition systems or high-energy ignition (HEI) systems do not require resistance in the circuit, so it is recommended that a harness modified for HEI be ordered if the ignition system has been upgraded. In most cases, these harnesses are available in our catalog and feature unique part numbers.