Photos from relay additions to both low- and high-beam headlights on my '88 K1500 using four sealed-beam headlights.
Installation would be very similar with two sealed-beam headlights, or four halogen-bulbs-in-composite-housings.
My vehicle had one especially-rotted sealed-beam reflector. I replaced that sealed-beam.
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On my truck, the headlight harness routes along the left fender just under washer bottle.
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Added a connector set so the headlight wiring can easily be returned to stock.
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Pulled power from the firewall-mounted distribution block. Could easily have used 16-gauge wire, except the smallest I keep on hand was 14-gauge. Two power wires, two ATO--ATC fuse holders, equipped with
SELF-RESETTING TYPE 1 CIRCUIT BREAKERS for safety, just like OEM breakers. Fuses pop, they're done. This will allow the headlights to flash if there's a fault, providing some light. A fault in either the low- or high-beam won't shut-down the other circuit--again safer than a single fuse or circuit breaker. All of this is covered by the OEM plastic shield (not shown) which will keep rain and road-splash out.
The low beam (two 55 watt filaments) is protected with a 10-amp breaker, high beam (two 65 watt filaments) is protected at 15 amps.
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Relay electro-magnetic coil ground supplied by sheetmetal screw, flat washer, star washer, and bare metal around hole in inner fender area.
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This photo shows the diode installed into the connector pictured above. Took a couple of extra days for the diode to show up. This is what keeps the low-beam lights lit when the high-beams are selected.
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Note that headlights are rated for FULL BRIGHTNESS at 12.8 volts. Higher voltage will increase the brightness. Headlights are rated for FULL SERVICE LIFESPAN at 13.2 volts. As a rule of thumb, increasing the voltage 5--6 percent above 13.2 volts will increase filament brightness by 20%, but will reduce the service life of the bulbs by 50%.
Ideally, the headlights run at or above 12.8 volts, but
not above 13.2 unless you deliberately choose to sacrifice bulb life. The challenge is not to get maximum voltage to the filaments, because you'll severely shorten their life!
Prior to installing the relays, I had about 12 volts at the light socket with the lights "on". With the relays I now have about 13.8 volts. That's more than I wanted, (probably should have used that 16-gauge wire instead of 14, for the main power to the relays) but still nearly 3/4 volt lower than the alternator output. The ground side of my headlight circuit is good--almost no resistance.
https://www.carlightblog.com/2012/0...-volts-high-on-board-voltage-short-lamp-life/
Having changed a damaged sealed-beam, added relays to increase available voltage to the filaments, added the diode to run all four lights when "high" beam is selected...
all I have left to do is to get them properly aimed.
[Edit] Oooops. Made a mistake. Forgot to insulate the two leads coming out of the diode. Gotta fix that as well. [/Edit]