1974 Under Dash Wire Harness (For Trucks With Warning Lights) – GM Truck This is your main under dash harness with the fuse block included. this harness connects to: the forward lamp harness at the firewall, the engine hanress at the firewall, the instrument cluster hanress, the taillight harness at the firewall, the windshield wiper motor, the windshield wiper switch, the ignition switch and the headlight switch. all of tuckers wire harnesses are made with the original blueprints, original connectors, and original color wire. this helps to assemle your truck’s wire harness per the factorywire diagram. the best thing about our hanresses are, they are made in u.s.a.!