The hazards, gas gauge, and heat on a 1987 Toyota 4Runner work because they are all powered by the vehicle's electrical system. The hazards are powered by the turn signal relay, which is located under the dashboard. The gas gauge is powered by the fuel level sensor, which is located in the fuel tank. The heat is powered by the heater control module, which is located under the dashboard.
If the hazards, gas gauge, or heat are not working, it is possible that the electrical system is not functioning properly. You should check the fuses and relays to see if any of them are blown. If any of the fuses or relays are blown, you should replace them. If the fuses and relays are not blown, you should take your vehicle to a qualified mechanic to have it diagnosed.
