In our July '07 issue, we showed the installation of Reen-machine's high-performance halogen headlight system that fits all '65-'68 and '70-'73 Mustangs ("How to Upgrade Your Headlights," p. 38). Those cars use a pair of 7-inch headlights, meaning they won't fit '69 Mustangs. They're the only vintage Mustangs that use four lights with separate high-beams.
After that story ran, it became apparent to Reenmachine that offering a four-light system for '69 Mustangs or any car that uses 531/44-inch headlights would be a good idea.
With that in mind, we headed to Reenmachine in Ventura, California, to show the installation process for putting the lights in a '69. The procedure is basically the same as for the two-light setups, save for the two additional high-beam lights and a few other tasks.
To refresh, there's more to it than putting new headlights on an early car. The electrical wiring wasn't designed to handle the power draw from modern halogen and Xenon headlights. That's one of the things covered here, since simply swapping a headlight isn't really much more work than changing a household light bulb.
The Reenmachine package consists of four Delta high-performance halogen H4 headlights and a modern high-output, relay-driven wiring harness. The key to the two- and four-light systems is the harness that bypasses the car's existing headlight wiring and employs the new wiring for a safe and effective upgrade. It's an outstanding setup and we were enthusiastic to show shop owner Pete Waydo installing the system on our '69 Mustang project car.
These days, bright headlights are available for any car. The trouble with classic Mustangs is the original wiring isn't designed to handle high-wattage lights. Another problem when using high-output lights is that the circuit breaker in the headlight switch can't handle the current. The cure for this problem is installing two relays, which are included in the wiring harness that comes with the Reenmachine package. The Delta lights also look good, as installed here in our '69 Mustang project car. | 
The Reenmachine custom lighting system is a plug-and-play setup that can be installed in about an hour. This version fits '69 Mustangs or any car that uses four 531/44-inch lights. The included wiring harness is plugged into the car's existing headlight harness via one of the old low-beam headlight plugs. From there, the harness is routed and connected to power and ground, then the headlights are installed. Some legs of the harness are extra long to accommodate various mounting locations and routing. If there's excessive leftover harness length, slack can be cut out and the wires can be respliced together. It can also be coiled up, tie-wrapped together, and tucked out of sight. There's plenty of room in the cavity behind the headlight buckets to hide the wiring. Reenmachine also preinstalls the H4 halogen bulbs in the Delta headlight housings prior to shipping the systems. | 
Installing the lights is just like changing a regular headlight. Begin by disconnecting the negative battery cable, then remove the rings around the low beams. They're held in place with three screws. |
Loosen the three screws holding the formed sheetmetal headlight retainer. This should allow you to rotate the retainer (its holes are elongated) and remove it from the car. If you have trouble, take out the screws altogether. | 
The old sealed-beam headlight should come right out and hang from the wiring. Unplug the bulb as shown and repeat on the other side. At this point, both low-beam headlights should be removed with the ends of the old headlight harness hanging out of the holes in the headlight buckets. | 
Removing the inner high beams on '69s is nearly the same as with the outer low beams. To access the high-beam lights, take out the screws in the plastic ring that attach it to the grille. |
With the ring out, the high beams are taken out the same way as the low beams: Either loosen the screws in the headlight retainer to rotate the retainer off the screws or remove them entirely. As with the low beams, the old high-beam bulb will come out and hang from the wiring. | 
Uncoil the new harness onto the floor and look it over. It includes the two relays previously mentioned, as well as a fuse. The harness has a male plug to connect it to the old harness and four female plugs that connect to the new Delta headlights. Find a good mounting place for the relays and fuse. It's unlikely you'll need to get to them later, but a suitable place for easy access is still a good idea. On our '69, we removed the battery to allow access and mounted the relays and fuse on the inner fender next to the battery. Use the supplied self-tapping screws to secure them in place. | 
This is how the completed installation of the relays and fuse in our subject car looks. Note the battery tray in the bottom of this photo. |
After the relays are in place, thread the part of the harness with the male connector to the passenger side low-beam headlight area. This will connect to the original low-beam female headlight plug. | 
Insert the male harness plug into the female headlight plug as shown. It must be one of the two low-beam plugs, and the passenger side is likely to be the best choice since it's close to the relays. | 
Next, attach the black wire of the harness to a good ground location near the passenger-side headlight area. You can also connect it to the negative terminal on the battery. |
It's necessary to enlarge the hole in the back of the metal headlight cup to clear the bulb and rubber boot on the back of the new headlight. You may be able "to do this with a large hole saw with the cup installed in the car, but it's likely easier to remove the cup and open it with a grinder or similar tool. Remove the cups as shown. | 
On '69 Mustangs, removing the front splash shields from inside the wheelwell makes access much easier for routing the harness. | 
With the splash shields out, run the harness so one female plug comes through the hole in the back of each headlight cup where the old plugs came through. The female plugs at each end of the new harness (with three wires each) are for the low-beam lights, and the other female plugs (with two wires each) are for the high-beam lights. The wiring harness is the secret to making the system work and negates rewiring the car. When the new harness is installed, it relegates the old one to only having to deal with low currents passing through the old wiring and headlight switch. The current now going through the old wiring only controls the relays which, along with the new wiring, now handle the current of the high-powered headlights. The three no-longer-used headlight plugs can be tucked away behind the headlight buckets. |
As previously mentioned, use a grinder to enlarge the holes in the four headlight cups. | 
Use a marker to indicate where and how much material needs to be removed from each cup. A completed one is on the left.c | 
Test fit the headlight into each cup before putting it into the car, then reinstall the cups using the original hardware. |
With the cups enlarged and harness installed, the new Delta lights are plugged in. This is one of the high-beam units. | 
With the high-beams in, reinstall the plastic trim ring that goes around the bulbs. | 
The low-beam Delta headlights are installed and secured into place with the original hardware. |
For '69s, the passenger-side part of the Reenmachine wiring harness can be routed to the driver side of the car in front of the radiator. A series of factory clips in the core support can be used to secure the harness in place. It's also a good idea to install a series of zip ties to further secure the harness. | 
Connect the power wire to the positive battery terminal or the hot side of the starter solenoid. Loosen and remove the nut on the solenoid, slip the eyelets onto the stud, and reinstall the nut. Check the entire wiring installation to make sure no wires are pinched, running over sharp edges, or otherwise at risk for damage. | 
Complete the installation by joining the main harness to the section that's connected to the starter solenoid. |