These days, bright headlights are available for any car. The trouble with classic Mustangs is the wiring wasn't designed to handle the high-wattage lights. Another problem is the circuit breaker in the headlight switch can't handle the current. The cure is to install two relays, included in the Reenmachine wiring harness. The flat-faced Hella lights look trick, as installed here in Pete Waydo's '66 Mustang.
Headlight technology of the '60s is nothing compared to what's available today. Similar to other automotive components such as tires, suspension, engine pieces, and safety equipment, headlights have improved in leaps and bounds since the first Mustangs were built in 1964.
Speaking of safety equipment, headlights are among the most critical pieces of safety gear on a car. Upgrading them is not only cool in terms of appearance and driving enjoyment, but they need to be done correctly for nighttime driving. Lights on most older cars are almost always lacking when it comes to nighttime driving.
After chatting around the editorial water cooler, we thought it a good idea to examine the subject of better headlights for vintage Mustangs. There's more to it than just installing new headlights on an early car. The electrical wiring isn't designed to handle the power draw of modern halogen and xenon headlights. Here we focus on wiring since swapping a headlight is little more than changing a household light bulb.
At one point, we were won-dering what path to take on this subject until we came across a custom lighting kit designed specifically for vintage Mustangs. Offered by Reenmachine, the package consists of a pair of Hella high-performance halogen H4 headlights and a modern high-output, relay-driven wiring harness.
The key to the system is a harness that essentially bypasses the car's existing headlight wiring and employs the new wiring for a safe and effective upgrade. We couldn't wait to get to Reenmachine in Ventura, California, to cover the installation on shop owner Pete Waydo's '66 Mustang six-cylinder coupe, which is driven daily.
The Reenmachine lighting system is a plug-and-play setup that can be completed in about an hour. It fits all '65-'73 Mustangs (except '69s-see the sidebar). The included wiring harness is plugged into the car's existing headlight harness via one of the old headlight plugs. From there, the harness is routed, connected to power and ground, and the headlights are installed. The various legs are extra long to accommodate mounting locations and routing. If there's excessive leftover harness length, slack can be cut and the wires can be securely respliced together-be careful to match the colors-or it can 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 wires. Reenmachine preinstalls the H4 halogen bulbs in the Hella headlight housings. | 
The lights themselves install just like changing a regular headlight. Begin by disconnecting the negative battery cable, then remove the headlight door for '65-'66s. It's held in place with four screws. The door comes off to access the headlight retainer. | 
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, completely remove the screws. |
The old sealed-beam headlight should come out and hang from the wiring. Unplug the bulb as shown and repeat for the other side. At this point, you should have both headlights removed with the ends of the original headlight harness hanging out of the holes in the headlight buckets. | 
Uncoil the new harness onto the floor and look it over. It includes the two relays previously mentioned, as well as a fuse. This is the main element of the harness. The rest includes a male plug to connect to the old harness and two female plugs that connect to the new headlights. | 
Find a good mounting place for the relays and fuse. It's unlikely you'll need to access them later, but a suitable place for easy access is still a good idea. On this '66, we mounted the relays and fuse below the battery. Use the supplied self-tapping screws to secure them in place. |
This is the completed installation of he relays and fuse in our subject car. Note the battery in the upper-right corner of this photo. | 
This opening in the '66-right above the battery-was the perfect place to begin routing the wiring harness. All three legs of the harness pass through on the way to their required locations. The two female plugs connect to the new bulbs, and the male plug connects to one of the original headlight plugs. Run the harness so each female plug comes through the hole in the back of each headlight bucket and the male plug is in the vicinity of an old headlight plug. For the cleanest routing of the new harness, you'll want to use the original passenger-side headlight plug near the relays and fuse. The male plug has already been passed through and will connect to the old one that came off the passenger-side headlight. | 
Once passed through, connect the male plug to the original female headlight plug-in this case, on the passenger side of the car. This is the secret to making the system work and negates any rewiring. When the new harness is plugged into the old one, it relegates the old harness to handling low currents. The current now going through the old wiring only controls the relays, which-along with the new wiring-handle the current of the high-powered headlights. The unused original headlight plug is tucked away behind the headlight bucket. |
The passenger-side female headlight plug is passed through the same hole in the inner fender above the battery then pulled through to the headlight bucket and attached to one of the new Hella lights |  | 
Once plugged in, the Hella light is reinstalled similar to any regular headlight. Reverse the removal of the old light shown in the first three steps. |
Just as on the passenger side, there's an opening on the driver-side inner fender to run the female connector through the opening and to the headlight bucket. | 
Once threaded through, the female connector is plugged into the driver-side Hella bulb. Once the bulb is plugged in, thread the excess harness behind the headlight bucket and into the fender, as is done here. The headlight is then installed and secured in place with the original hardware, and the headlight door is reinstalled. | 
With the passenger-side light, relays, and preliminary harness routing completed, move to the driver side. This includes routing the driver-side connector underneath the radiator. We were able to get this leg of the harness inside the core support, run it underneath the radiator, and have it come out of this opening next to the driver side of the radiator. |
Once the headlight was plugged in and installed and the excess wire was tucked into the fender, we went back to secure the underhood section of the harness with tie-wraps. Although the old headlight harness is no longer used, it still serves a purpose as a place to securely attach the new harness. | 
Here's the new wiring harness tie-wrapped in place to the old headlight harness. This is the section of harness running from near the driver side of the radiator to the opening in the inner fenderwell. | 
'69s Too
The Reenmachine headlight package fits all years of vintage Mustangs except '69, which is the only year Mustang that used four smaller 5-3/4-inch lights instead of two 7-inch ones. Never fear though, because Reenmachine has been thinking about developing a '69 system for some time. When we suggested we help develop it-and had the car-shop owner Pete Waydo expressed interest.
After taking our trusty '69 Mustang project car to Reenmachine, the result is four Delta headlights (www.deltalights.com) that will fit '69s: a pair of low/high beams and a pair of highs. The wiring harness Pete researched and assembled worked perfectly, and it was similar to installing the harness in a two-light system. There are differences, though, and we'll show the full installation process in a future how-to article. One is that three original headlight plugs are retained rather than one, but otherwise the wiring is basically the same. We can also tell you the Delta lights are absolutely spectacular, and hitting the high beams is like having full daylight right in front of the car. Look for the four-light '69 system to be available from Reenmachine later this year. |
With the headlights and harness installed, all that's left is to connect the power (red) and ground (black) wires. An eyelet is attached to the red power wire. Attach another eyelet to the ground wire. | 
Connect the black wire to the negative battery terminal or other good ground. Be sure your ground connection is solid as electrical problems are often traced to poor grounding. | 
Complete the installation by connecting the power wire to the positive battery terminal or the hot side of the starter solenoid, as shown here. Loosen and remove the nut on the solenoid, slip the eyelet onto the stud, and reinstall the nut. Check the entire wiring installation to make sure no wires are pinched, running over sharp edges, or at risk for damage. |