GTO Lighting Harness Fix
Replacing a GTO front lighting harness
Story Jim McGowan - June 19, 2011 09:00 AM
I replaced the original engine wiring harness in my ’70 GTO Judge with an exact duplicate from M&H Electric Fabricators and was very pleased with the results. Now it’s time to replace the front lighting harness with a new one from M&H as well (part #13635 for Ram Air).
The best part about these harnesses is they fit perfectly and use all the same connectors as the originals from GM. No cutting, soldering or splicing is required. Both of these harnesses are removed and replaced almost exactly, depending on your options, for the 1968 through 1972 GTO, LeMans or Tempest. There is a difference between Ram Air and non-Ram Air harnesses, so specify your engine and options when ordering.
The lighting harness is a little more difficult to install, as it must be snaked through some tight places. Obviously, it would be much easier with the urethane nose off the car, but that is really a pain. The front end on this car is lined up too nicely to fool with it. So, I will install the harness with the nose in place.
The degree of difficulty is not that great if you simply take your time. I took about an hour and figured the best way to approach the removal and replacement. By fitting the components on the new harness through those tight places to make sure they would clear, a lot of wasted time and headaches were avoided.
Disconnect and remove the battery; you’ll need that area empty to work with the wiring. To access the front work area, you will have to remove the filler panel at the top, the front grilles, the headlights and turn signal lights. All this took about an hour. No special tools are necessary and small hands are a plus. I started by unplugging all the wire connectors from the bulbs and side marker lights.
There are also two ground wires under each front fender at the core support. These are a little tough to access but you can do it! With all the connectors free, I pulled the wiring through an area at the bottom of the nose-mounting bracket. The three-prong headlight connector has to be worked through but the rest simply come right out. Then disconnect the horns. The harness in this car was lying at the bottom of the radiator instead of in its original holders at the top of the core support. After a repaint years ago, the body man neglected to put the harness back in the clips while replacing the nose. Rather than fight all that wiring through the second nose support and up through the core support, I cut it just before it passed through the support. Then it comes out through the grille opening.
After disconnecting the second set of ground wires under the driver’s side fender, removing a plastic plate in the core support and unplugging all the connectors, the rest of the harness can be pulled up from under the fender and through a rectangular hole in the support. The photos show this access hole.
Now to the bulkhead plug. Loosen the 3/8-inch bolt securing the large wiring plug to the firewall and pull the plug out. In this case, the engine wiring plug is new, and the lighting plug is original. The lighting plug slides out of the larger engine plug. Disconnect the wiring from the horn relay and unplug the wire at the brake distribution block on the frame. Now you can remove what’s left of the old lighting harness.
Ready to Re-wire
I started the install at the same place I started the removal, at the passenger side of the nose. I snaked the new wiring and connectors through the nose support bracket from the empty grille hole, reached through the directional light hole to get them, and let them hang out the light sockets. Then I placed the new wiring into the factory holding clips working toward the center support. The two ground wires need to be pulled up through the hole on the core support but there is no way to reach that high through the turn signal light opening. I used a test wire with alligator clips at each end to do this. I fed the wire through the access hole from the engine side, and connected the clip to the ground wires ends. Then, I carefully pulled the wires up and through the hole to be reconnected. This worked well.
Moving toward the driver’s side, I first wrangled the bulkhead plug, still wrapped in plastic, through the space at the nose support bracket. This took a little doing, but it went through after a few tries. Then the rest of the connectors were pushed/pulled through. Using a little body English, I reached under the fender while pushing the bulkhead plug up with my arm in the directional light hole. This worked just fine and I’m only on cut number five. Ya gotta bleed a little! Pull the plug and ground wiring into the engine compartment and set it aside for the moment.
Now connect all the bulbs, etc., on both sides to the harness and reinstall the headlight bulbs with the retaining rings, directional lights, etc. Then reconnect the two ground wires under the driver’s side fender and move back to the firewall plug. Install the lighting plug into the engine harness plug and reattach to the firewall. Don’t overtighten the 3/8-inch bolt or you might break the plug case; just seat it to the firewall snugly. Then connect the two wires to the horn relay. They will only go on the correct terminals, so no worries. Reconnect the wire to the brake fluid distribution block. Now you can reinstall the battery and connect the cables.
Here’s where I ran into trouble
All the lights and horn worked perfectly except the directional signals. NO light there at all. I checked power at the socket and it was fine. So I compared the original socket to the new socket and found the problem. The original sockets have two connector spades in each that must be removed and transferred to the new sockets. They simply pull out and push in. After I did this, both directional lights fired up and everything worked. The removal and reinstallation took about four hours working slowly as to not amputate any body parts. The new harnesses look great and fit perfectly.
Since a picture saves a thousand words, check the photo sequence and you’ll find a few tips that will make the job easier.