Most Corvettes can benefit from a headlight upgrade. After all, the better your headlights the better you can see at night and the safer you are. For many people, a headlight upgrade means HID or some other conversion that may (or may not) be legal and which often delivers a retina-searing blast of white light toward oncoming drivers, making it difficult for them to see the road. While it may be useful to have a set of driving lights set up like that, for day-in, day-out driving, the better answer is probably somewhere between that and the factory bulbs.
In the case of the C5, it’s not just the inevitable aging and fading of the 20-year-old lamps that hurts them, it’s also because Chevy could have done better at the time. Factory lamps for domestic-market Corvettes were originally designed for the 1992 Cadillac Seville, a fine car I’m sure, but not one expected to be driven enthusiastically through the mountains. The good news is that export C5s came with better lights that combine H4 halogen bulbs with Bosch metal reflectors and glass Guide lenses that provide beams that are wider, brighter and better focused.
However, it’s not just as simple as finding export lamps. The reflector housings are made for both right- or left-hand driving, and using left-hand headlights here in the U.S. is unsafe. To get the correct, right-hand export components, we reached out to Daniel Stern Lighting Consultancy for a pair of the correct housings as well as the bulbs and a relay kit containing the components needed to assemble the wiring harness to power them. While Stern offers professionally built harnesses, we’re wiring nerds and prefer to do it ourselves.
Instructions came with the parts we ordered, but for those who haven’t done much electrical, there are a few things to be aware of and the first is the use of relays. A relay is basically a switch that you turn on, which then allows power to pass through it to go somewhere else. Typically, the power for a pair of headlights goes through the headlight switch that, when turned on, allows the power to go to the headlights. It’s a long path for the electricity to follow and every bit of power that gets to the lights has to go under the dash and through the headlight switch, places where you really don’t want a lot of amperage. This is especially a problem on older cars.
A typical relay setup, however, draws power directly from a source such as the battery or alternator and sends it to the bulbs, with the original output wires from the headlight switch only serving to “turn on” the relay and allow the power to pass through it. The power through the relay usually comes through a shorter, heavier gauge wire, which also helps deliver more power directly to the bulb. For example, the factory wiring to each bulb on a C5 appears to be 16-gauge. We fed the relays with a much larger 10-gauge wire and then each individual bulb with 12-gauge. We used two relays (one for high beam and one for low) and located them on the passenger-side of the car close to the battery box, from which we drew power.
The factory headlights have two plugs on each light: one that goes to the high beam bulb and one to the low, for a total of four plugs. Each plug has two wires, a power wire (green for the high beam bulb, brown for low) and a ground (black on both). The new H4 bulbs, however, use a single bulb per side with a three-wire plug that has a power wire each for high and low beam (green and brown) and a black ground wire. To wire the new plug, the power wires will come directly from each of the two relays and the black ground wire will need to be grounded from the plug to the frame.
Since the relays are located on the passenger-side, that means snaking the long harness of three wires and the plug across the nose of the car to the driver-side. We used zip ties to attach the harness to the bolts protruding downward from the bodywork just forward of where the hood sits when its closed, where it’s out of the way and unobtrusive. You’ll need to measure this distance before wiring the relays so you’re sure to have enough wire length, and don’t forget to include an extra loop of wire on both sides to allow the headlights to go up and down.
Disconnect the battery prior to starting work, and once the lights are installed and working, don’t forget to follow Stern’s instructions and have them correctly aimed to get the most out of them. Vette
1. Headlight disassembly should be familiar for anyone who’s ever changed their bulbs. Start by raising the headlights, which you can do by turning the grooved knob on the headlight motor assembly and then removing the screws that hold the plastic bezel surrounding the lights.
2. With the plastic bezel out of the way, you have access to the Torx screws holding the body-colored headlamp door in place.
3. The headlight assembly has three molded-in alignment studs that fit into holes in its metal bracket and is screwed in place with three self-tapping screws: two on the outboard side, one on inboard. The two outboard ones on the passenger’s side are visible in this photo, shown from the front. The screw heads are hard to get to, so we strongly suggest a ratcheting wrench. Our screws had pieces of the headlight’s plastic housing still stuck in the threads after removal, so make sure the threads are cleaned out prior to reassembly.
4. The upgraded headlight assembly uses an H4 halogen bulb with an entirely different plug than the stock C5 headlight so there’s going to be some wiring involved in getting this to plug in.
5. Although the headlamp housing in our kit came with bulbs already installed, we ordered the upgraded Osram bulbs to go with it. The standard-wattage Osrams offer better seeing distance and beam focus, and run a bit over $40/pair.
6. There are two different types of H4 plugs available from Stern: a phenolic plug with a pigtail that needs to be spliced on and a heat-resistant ceramic plug, which is the one we selected. It’s a bit of a bear to install, as standard crimpers can distort the terminals and the ceramic can be easy to break but we took our time and also soldered the connection. We ordered a spare set to replace the one we bent beyond repair.
7. The Flosser use the standard Bosch designations (30 for power input, 85 for trigger ground, 86 for trigger input, and 87 for power output) and have two output terminals—one for each side of the car. You’ll want to keep an eye on the plug as you wire it to make sure you’re plugging things into the correct terminal, and remember there’s a separate relay for high beam and for low.
8. The plugs are grooved so they can be mounted together as one unit, and the relays come with a thin, bent metal bracket that can be slid into a matching recess on the back of the relay. While we considered mounting the two relays together as a unit, that would have required fabricating a bracket, so we took the easy way out and mounted the relays separately by the metal tabs.
9. Each relay will be fed with a heavy-gauge wire (we used 10) from the battery, and each will need to be fused at 20 amps. The kit came with these weathertight fuse holders. To install them, we clipped the red-insulated wire and spliced one end to the main power wire and crimped a ring terminal on the other.
10. We replaced the terminals that came in the kit with these strain-relief ring terminals, which have a second set of prongs that are crimped onto the insulation for a more secure, longer-lasting connection. After crimping on the terminal, we sealed it up with 3M adhesive-lined shrink tube. The terminals came from Mouser, the tubing from Waytek.
11. The most easily reversible way to wire the lights is to use the included adapters that plug directly into the factory bulb connectors and wire them to trigger the relay. You never cut the harness, and it can just as easily be unplugged and removed if you want to return to the factory lights.
12. The cleaner way, however, is to remove the sub-harness that goes to the bulbs and build a new one that will go from the main lighting harness to the relay. This is where the sub-harness plugs in, right next to the headlight actuator. Note the three visible wires: black, green and brown. These are the ones that matter to us.
13. The three terminals of the sub-harness plug into a five-way Metripack 280 connector: the other ways contain the wiring for the actuator that raises the headlight. We removed the black secondary lock from the connector and used our Metripack pin removal tool to gently remove the three headlight wires, being careful to note which of the pins went into which way.
14. We then created a new sub-harness with 16-gauge wire in the correct colors, using the correct grey wire seal and Metripack 280 terminals so we can plug it right back into the connector. (For those unfamiliar with assembling Metripack connectors, we covered that in the Scarlett project in some depth) The green wire serves as a trigger wire for the high beam relay, brown for the low, and the black wire, which we spliced into two separate wires, serves as a common ground for each of the relays. All wires were then routed through heat-resistant fiberglass conduit similar to what the factory used.
15. This steel bracket is conveniently located directly beneath the passenger-side headlight assembly. We mounted the high beam relay to it by simply removing the existing nut, opening up the hole on our relay mounting tab, then slipping it on the threaded stud and reinstalling the nut. The low beam was about as easy: we added a second nut so the body of the relay would clear the molded lip at the bottom of the bracket.
16. To make the installation as unobtrusive as possible, we routed the power and ground wires through the same type of heat-resistant conduit (we had two sizes on hand) and ran it beneath the surge tank located on the passenger side. The tank is easily removed and should not have to be drained if you’re careful enough not to knock any of the fittings loose. The two main mounting studs are visible in the lower part of the photo, and the two plastic prongs on the lower left of the tank are clamped in place by a third nut visible directly beneath the prongs.
17. The bulb ground wires were connected to this ground stud located beneath the battery box, which should be loosened to give you access to the stud. Note the conduit containing the main power wires for the headlights: it enters the battery box at the same place.
18. The main power wires were routed behind the underhood fuse block located in the battery box and mounted to the stud where power comes into the fuse block. In a perfect world, we’d have powered the lights using one of the two existing, unused Maxi-fuse ways in the fuse block, but that was a bit deeper into the car’s wiring than we wanted to dig.
19. After installing the passenger-side headlight, but prior to replacing the driver-side. The new light produces a much cleaner, brighter light than the dirty yellow illumination from the factory lights, but without blinding those in oncoming lanes.
Photos by Jeremy D. Clough