Headlight wiring gauge? – Ford Truck Enthusiasts Forums

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+61404532026, 04:31 PM

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Headlight wiring gauge?


As I do my 2005+ headlight upgrade, I also want to do an electrical upgrade to make the headlights brighter.

I want to put relays in, instead of pumping all the current through the headlight switch and high beam switches.

.

Low beams separate in the engine bay fuse panel to feed separate 10 amp fuses.

High beams separate at a splice point in the main harness.

I had planned on running 12 AWG wire, which I know is WAY overkill as it normally supports over 20 amps. I’d like to reuse as much of the factory wiring if I can so that I don’t have abandoned wires floating around.

Does anyone know what gauge wires Ford used for the Low Beam and High Beam feeds to the headlight connectors? I feel that 14 gauge should be fine.

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+61404532026, 04:58 PM

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+61404532026, 05:30 PM

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If you really feel you need to do this… just put relays in underhood and re-route the wiring from the headlights to the relays.

-run new supply voltage from your battery to power the relays whatever gauge you want

-run new output wiring whatever gauge you want to the headlights

-switch the relays with your “old” factory headlight wiring

But honestly what will you gain? I don’t think you will notice even a slight difference. Simply check it this way: Put a voltmeter on your headlights (test both high and low and use the headlight + and -, do not use a direct body ground to check) while engine is running. Then voltmeter the battery itself (still while engine running). Is there any difference at all? If you see a difference of 0.2v or something like that then the difference will not be visible to the naked eye, just a bunch of work.

Ford wiring to headlights would be 16awg or less. But individual runs likely. There is a whole lot more to determining “amperage on this wire” than just wire gauge alone. Ground return path, wire length, voltage, all play factors when OEMs decide what size of wire to use. I did this for a living for 7 years so speaking from experience.

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+61404532026, 05:44 PM

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+61404532026, 05:59 PM

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Originally Posted by holeshotwalt

If you are talking about putting in higher wattage bulbs, then yes consider putting in relays. The ford system was never designed for a higher wattage bulb. Regular bulbs…. just cant see it making a difference.

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+61404532026, 06:19 PM

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Originally Posted by 03X

If you are talking about putting in higher wattage bulbs, then yes consider putting in relays. The ford system was never designed for a higher wattage bulb. Regular bulbs…. just cant see it making a difference.

Check ypur voltage drop. Regardless of the bulb you use if it only gets 95% of its rated voltage the bulb will only produce 83% of its rated lumens. If the bulb gets 90% of its rated voltage it only produces 67% of the rated lumens.

So if the bulb is was getting 11.5v instead of 12.8 you are loosing about 1/3 of the bulbs lumens.

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+61404532026, 07:00 PM

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“Voltage drop” and how to test for it is widely misunderstood. It’s always done while the circuit is under load (headlights on, for example).

One probe is placed on the negative battery post. The other is placed anywhere along the way, up to and including the negative connection at the headlight bulb. The voltage drop will express itself as a positive number and is of course cumulative. It’s showing the actual voltage lost in the circuit to corrosion and resistance. The drop at the battery, or at the headlights across + to – is not quite the same thing.

Of course Zero voltage drop is ideal, but about +0.1 volts – one tenth of a volt – is considered OK. Then do the same for the positive side of the circuit. About +0.2 volts for the positive side is OK. The total voltage drop should not exceed maybe +0.4 volts.

These are easy tests and don’t require disassembly.

With all that, I’m surprised that a 2005 vehicle doesn’t have OEM headlight relays?

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+61404532026, 09:49 PM

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Originally Posted by pirate4x4_camo

That’s exactly what I was trying to do, except I wanted to use the factory wiring. I don’t like abandoned wiring laying around in engine bays.

The other solution is to remove the harness, unwrap the 16 yr old tape, and strip out the unused wires.

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