How to get Brighter Headlights

  1. Joeychgo
    It takes more than a powerful alternator, and more than changing to powerful replacement headlights, to get brighter headlights on these older cars and trucks.


    The above photo was taken with High Beams ON, and the engine was running at highway cruise RPM. 14.1 volts measured at the Horn Relay was perfect. (It’s the main power distribution buss-bar in this electrical system.) But the headlights were only running at 11.5 volts!

    The voltage drop to the headlights in the above measurements was typical, as the headlight system on many cars is under-wired

    The headlights on our older cars and trucks are not very bright. They weren't when these cars were new. But when those cars were new, we didn't have anything better to compare our lights to. So the dim headlights were accepted as normal. Nowadays, many people replace the old headlight sealed beams with more modern HALOGEN replacements. It's true that the halogen's do not look yellow at low voltage, like the old sealed beams did. But the HALOGEN replacements also do not produce maximum illumination when operating at low voltage.

    Thinking of popping in killer European H-4 headlights? Unless the "real problem" is fixed, those powerful replacements will only compound the built-in deficiency. That's true because they will draw more current, resulting with even greater voltage drop in the "under-wired" factory system.

    Furthermore, Our American made cars and trucks have had automatic-reset circuit breakers built into the headlight switch for many years. And the circuit breaker is not rated for the greater current draw of those powerful H-4's.

    Many owners of Ford cars and trucks, built in the '60's and '70's, especially with the four headlight systems, are familiar with the headlights flashing OFF and ON. (Like erratic Morse Code, after driving awhile on High Beams.) The problem occurred because the circuit breaker in the headlight switch was weak. Simply installing H-4's in most of our older cars and trucks will result with the same effect known to old Fords. (The circuit breakers in original factory headlight switches cannot handle the extra current draw of the more powerful headlights.)


    Lighting systems engineering data has it that if we drop the voltage delivered to a light by 10%, then illumination out-put is reduced by over 30%. Going from 14.0 volts down to 11.5 volts is a loss of nearly 18%! As we shall see in photos–No wonder those old cars and trucks have dim lights (when factory equipped). The goal with electrical systems is to keep voltage drops within a 2% loss.

    If you're wondering how much the up-grade would help your favorite car or truck, it's really quite simple to do as we did and take measurements with a VOLTMETER. (The photo captions explain the voltage measurements recorded by these photos.)

    If voltage measured at the back of the headlight, with High Beams ON, and engine running at highway cruise RPM, is less than 13.5 volts–Then this headlight/relay up-grade will be an improvement. Most factory built cars and trucks will not perform better than 12.0v - 12.8v range, and many will drop below 12.0v, even with perfect factory wiring.

    TIP: The meter wires must be connected to the head light terminals with the car's wire harness connected to the headlight. Even with "two headlight" systems, the High Beams are higher in wattage (they draw more current), and so the system should be tested with High Beams ON.

    In photos and captions, here are the before and after the test voltage measurements at key parts of the electrical system.


    High Beams ON, Engine running at highway cruise RPM. (Photo taken indoors, evening, the hood was blocking overhead shop lights–so the powerful camera flash "strobe" froze the alternator fan as if it was still.) The Alternator system is working perfectly–that's definitely not the problem.

    This car was previously up-graded to a GM DELCO, 63amp, model 10SI, built-in voltage regulator system. It is properly wired using M.A.D.'s part # ALT-1, Alternator Wiring Kit. The kit's new 8 gauge wire is routed from the alternator directly to the horn relay buss-bar.


    High Beams ON, plus heater fan ON medium speed, plus windshield wipers ON, Engine running at highway cruise RPM–barely over 11 volts at the dash!


    The more switches we turn ON, the lower the voltmeter shows. The dash-mounted voltmeter gives us the indication that the alternator is not able to keep up with system demands.

    But, we went back to the alternator, and to the battery, and to the horn relay buss-bar, (the "key check-points") and rechecked voltage levels. With the engine running at highway cruise RPM, lights, heater, and wipers ON, we had 14.1 to 14.3 volts at all the "key check-points" under the hood. (Which is perfect.)


    Sometimes in attempt to learn, "Just who is telling the truth here?"–It's a good idea to get second and third opinions. Ha! It turns out that all three voltmeters gave us pretty close to the same story.

    We got out another digital voltmeter, and connected two digital voltmeters to the stud terminals at the back of our dash mounted voltmeter, and ran the engine at highway cruise RPM, no lights or accessories ON.

    The digital meter on the left is actually the most accurate of these three. It was by far the most expensive. A reputable company, which calibrates and certifies diagnostic equipment, has checked it. And its readings are always consistent with other "high-end," expensive meters. Also, when switched to 20v, it measures to the nearest 1/100th of a volt.

    And, after this photo was taken, we did switch the lights ON, and the heater to medium, and found that all three voltmeters dropped back down to less than 12 volts. But yet, under the hood still showing 14 volts.

    Well now, what we have going on here is "voltage drop," in the factory wiring, to the dash area. The wiring in the car was inspected, and found to be in perfect condition–the problem is with design, not with defective parts or wiring!


    We even looked at the factory wiring diagrams, and found that the "battery live" buss-bar behind the fuse box was directly connected to the dash area "main feed wire."

    So, we could read voltage at the dash area main feed wire, from the fuse box, and we did. High Beams ON, heater fan on medium, engine running at highway cruise RPM. We measured only 11.22 here, (still with over 14 volts under the hood). Yep! We definitely have voltage drop in the dash main power-up circuit. And the same wire powers-up the headlight switch!


    The term "buss-bar" means a "common" connection, where wires all connected to the same circuit can come and go.

    "Junction block" is another term often used to describe this function.

    On our project car, the alternator output wire is routed directly to this buss-bar. The dash area main power-up wire originates at this buss-bar. The battery charging wire is connected at this buss-bar. And, the voltage regulator takes "sensing voltage" reading here, and adjusts alternator output to maintain voltage level at this buss-bar (14.0v to 14.5v).

    And now, a test of performance
    after adding RELAYS for the Head Lights


    Relays can be used as "remote control switches." It takes only a tiny amount of current to turn the relay ON. But when switched ON, the relay delivers power directly to the accessory. ("high gain" operation)

    We can install headlight relays next to the main power distribution buss-bar at the horn relay (where the old voltage regulator was).

    The factory "front lighting system" wire harness is routed just above that area, in route to the headlights. We can cut and detour the factory High Beam wire and Low Beam wire to the relays, and now the factory system will only have to switch the relays ON, instead of directly powering-up those big headlights.

    The headlights are up front, and the alternator is the source of electrical power; and the alternator is mounted at the front of the engine. It’s logical and sensible to mount RELAYS up front. Use existing wiring to switch the RELAYS ON, and then the relays will send full power to the lights. (And use of the relays takes headlight current load away from the dash wire harness, and so the ignition and entire electrical system will benefit too.)


    This test was done after the relay up-grade, with High Beams ON, engine at idle RPM. 14.0 volts measured at the horn relay buss-bar. 13.96 volts measured at the back of the headlight. (Before the relays, we had only 11.5 volts at the headlight, with 14.1 at the Horn Relay, at highway cruise RPM.)


    This test was done after the relay up-grade, with High Beams ON, engine at highway cruise RPM. (And it's a good thing our testing is finished, because the engine is warming up with so much "running in place.")

    With the current load to support the headlights removed from the dash wiring and switches, we took away the voltage drop in the wiring to the dash area.

    Now the dash mounted voltmeter will no longer "lie" to us when we switch the headlights ON. The ignition will not become weak. The dash lights will be brighter. And other accessories will be more powerful too.

    The first time the car was driven at night, the improvement in the headlights was remarkable! Now the lights are very bright.

    Everyone who has used our relay kits for the headlight system agrees that this is absolutely the best-for-the-money electrical up-grade. It adds reliability too, by removing current load from weak factory connections and switches. Considering the years of hassle free service, enjoyment, and safety, this is without a doubt the most sensible up-grade possible. It beats out expensive and often over-promoted luxuries like big sound systems, racing ignition systems, "high-end batteries," chrome alternators, and gadgets.

    Overall, the headlight relay up-grade makes these old cars and trucks more useful and enjoyable to drive.

    Two of our part # RLY-1 Relay Kits are required for the headlight system up-grade–ONE for LOW BEAMS, and ONE for HIGH BEAMS. (Even with "two headlight system" cars.)

    And for people who would like to learn more about electricity, voltage drop, assembly craftsmanship, Fusible Link wires, and more, we offer the "tech is made simple" book. The book is easy reading, and it's filled with great photos of craftsmanship and wiring techniques. Fundamentals of electricity are explained through cartoon-like illustrations.


    (The switch shown in the photo was removed from a FORD car. We ground off the rivet heads, punched out the rivets, and pried the cover from the switch, for a look inside.)

    Call-out labels with arrows point to various parts of the two circuit breakers in a typical headlight switch, shown in the photo above.

    A = Battery live "buss-bar," which also serves as mounting for the stationary contact points of the circuit breaker.

    B & C = Circuit breaker contact points.

    D & E = Resistance calibration notches in the movable arm part of the circuit breaker.

    F & G = Movable arm, metal strip, part of the circuit breaker.

    (Article from - Mad Enterprises)

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