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A Quick and Easy Headlight Upgrade

Making More Perfect Illumination

Robert Cassell Jan 1, 1998

Step By Step

With the headlights on and the engine running at highway rpm, the dash-mounted voltmeter showed barely more than 11 volts.

Even though low voltage was indicated at the dash, a voltmeter showed good output from the alternator (measured at the BATT stud) with the headlights on and the engine running at highway rpm.

The voltage at the horn relay buss-bar was 14.1 volts, but the voltage at the sealed beam was only 11.4 volts with the factory system. This measurement was taken with the headlights on, the engine cruising at highway rpm, and the meter connected to the low-beam wire.

M.A.D.'s Mark Hamilton also checked the voltage on the dash at the battery live terminal of the fuse box to see how the ignition system and the rest of the electrical system was functioning. This measurement was taken with the headlights turned on, the engine running at highway rpm, and the defroster fan switched to medium speed. The low meter reading indicated that the ignition and other accessories were not performing as well as they could.

With the relay installation complete, Hamilton rechecked the voltage at the horn relay buss-bar and the sealed beam. This time with the high beams powering up all four sealed beams, he measured 14.00 volts at the horn relay buss-bar and 13.96 at the sealed beam. That means we have only a 0.04-volt drop to the sealed beams with the new relay system, resulting in much brighter headlights.

Hamilton installed the M.A.D. relays on the radiator core support near the horn relay. The metal bar with two screws on the horn relay serves as the main power distribution for the entire electrical system, and the alternator output wire connects here, too. This was the perfect place to connect the main power-input wires to the new relays used for headlights.

Even with a powerful alternator, the lights can be dim, the ignition system can be weak, and the accessories can be lazy. M.A.D.'s Universal Relay Kit can improve any of these systems (two kits are required at $24 each for high- and low-beam headlight systems). The kit includes a heavy-duty relay, a prewired relay-harness connector, tinned copper-wire terminals, 3M shrink tubing, M.A.D.'s Tuff-Wire for main power delivery to the relay and to the output "load" circuit from the relay, and a fusible-link wire kit for short-circuit protection. The manual offers several pages of basic engineering information about relays and construction of heavy-duty circuits. Also in the manual is a long list of easy-to-follow diagrams for specific applications, including the brighter headlight system we used on our '65 El Camino. CHP

Improved Wiring

There are some things you just put up with on older Chevys. Many of these idiosyncrasies are so subtle that you may not even be aware of them. Take headlights, for example. You hit the switch, and they come on. But have you ever strained to look past your headlights on a dark, moonless night when the stock headlights just aren't enough?

While brighter halogen headlights are a help, the real culprit is a serious voltage drop between the alternator and the headlights. The good news is that the fix is quick, easy, and inexpensive.

Factory Wiring

After studying the original circuits, the length and gauge size of wire used, and the many electrical connections, it's easy to recognize that some of these parts are less than perfect. For example, even after you install a more modern, high-output alternator on an early Chevy, the battery voltage may be maintained at 14.2 volts, yet the headlights operate at only 11.3 volts. This substantial voltage drop results in dim headlights. The headlights, the alternator, and the battery power distribution are all mounted up front. But factory routing takes power from the front of the car, through the harness at the driver-side front fender area, through the firewall (entering behind the fuse box), up to the headlight switch, through the headlight switch with an internal circuit breaker, through the dash harness and down to the floor-mounted dimmer switch, back up to the firewall connector behind the fuse box, and back through the headlight harness to the front of the car. That's a very long circuit, and those factory wires are not heavy-gauge size.

So why not install a relay at the front of the car? Let the factory circuit turn the relay on (which takes around 0.10 amp), and the relay would serve as a heavy-duty remote switch, delivering battery power with full alternator voltage directly to the front lighting system.

For those of you not familiar with relays, they use low current to connect a high-current-draw component to a main power source, minimizing the need for long wiring circuits of large-diameter wire. Place the relay close to the load source and use heavy-gauge wire to connect them together. Then a small trigger wire is all that's needed to turn on the system.

It turns out that M.A.D. Enterprises, a company that specializes in electrical system upgrades, offers a kit to power up headlights, electric fans, fuel pumps, and other automotive electrical-system features using relays. The relay package comes complete, is easy to install, and includes a great instruction manual. And, most importantly, the brighter-headlight upgrade provides greater driving safety at night.

Improved System

The diagram above shows a more direct circuit between the alternator and the dash area, and it is wired with much heavier wire. Most old factory wire was only 12 gauge. We have shortened the wire and upgraded it to 8 gauge.

With Relays Installed

The system can be further improved by adding M.A.D.'s relay kit to the headlight circuit. After you install relays to power up the headlights, the relay mounted under the hood will handle the current load for the headlights. Headlights typically draw 12 to 14 amps. But with M.A.D.'s relay system, the dash wiring, headlight switch, and dimmer switch power only the relay. Turning the relay on requires about 0.10 amp.


M.A.D. Enterprises
Springville, CA 93265
(559) 539-7128

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