Replacing a heater core on a 1985 Nissan 720 pickup involves removing and reinstalling several components under the dash, including the instrument cluster and climate control assembly, as well as draining the coolant from the system. The task requires detailed knowledge of automotive mechanics and electrical wiring. While possible to do it yourself with adequate preparation and knowledge, it may be challenging for someone with limited automotive experience. Professional assistance or detailed DIY tutorials might be a more reliable option.
