My friend had a 1974 Firebird, he bought a 1979 Trans Am shell and transferred everything over from the 1974. A big difference is the 74 only had 2 headlights and the 79 has 4. He had been using the 74 harness to run 2 of the 4 lights. He bought a new 79 harness to try and run all 4 lights. The plug at the firewall was different, but the wires were all colored the same so we spliced the old plug on the new harness. We verified the same color wires went to the same lights on both harnesses as well. Setup this way, only the marker lights and turn signals work, none of the headlights will come on. There was power to all the lights(checked with test light, probably should have used voltmeter) and the grounds were good. We put the 74 harness back on and everything still works that way, so we know the lights and switches all still work. Open to thoughts/ideas, other things to check.
My friend had a 1974 Firebird, he bought a 1979 Trans Am shell and transferred everything over from the 1974. A big difference is the 74 only had 2 headlights and the 79 has 4. He had been using the 74 harness to run 2 of the 4 lights. He bought a new 79 harness to try and run all 4 lights. The plug at the firewall was different, but the wires were all colored the same so we spliced the old plug on the new harness. We verified the same color wires went to the same lights on both harnesses as well. Setup this way, only the marker lights and turn signals work, none of the headlights will come on. There was power to all the lights(checked with test light, probably should have used voltmeter) and the grounds were good. We put the 74 harness back on and everything still works that way, so we know the lights and switches all still work. Open to thoughts/ideas, other things to check.