My 2021 F250 XL was chewing through halogen headlight bulbs about every other month. Granted, I use them whenever driving, but that averages around 8-10 hours per week.

In rummaging around online, and [lurking] reading discussions on here about LED options, I came across an LED manufacturer's website that said they had found that the 2020-2022 (or -2023?) F250/350 Super Duties often had excessively high voltage at the headlights. If I remember correctly, they reported measuring, themselves, up to something like 18V or 20V. Their conclusion was that this is what was killing their previous generations of LED products, and what drove them to redesign their bulbs to handle anywhere from 8-10V at the low end to 40ish V at the high end (I'm guessing with an integrated buckboost, or something similar).

Out of frustration with my own bulb-binging problem and curiosity as to how in the world that could happen, I disconnected my upper passenger side bulb and stuck two thumb tacks into the sockets of the plug. I started the engine and let it idle, and then, despite measuring 14.4V or 14.5V at the battery terminals, I got a solid 15.4V at the headlight bulb plug. A neighbor, who is a true car guy, brought his own multimeter over and got the same readings.

How in the bloody hell could the voltage at the headlight bulb plug be greater than that at the battery terminals / the steady state voltage being produced by the alternator? Shouldn't the bulbs be operating at the charging system voltage, minus losses through harnesses & switching? Would Ford have bothered to run a voltage boost to headlight bulbs to gain ~0.9V (~6.5%) driving standard halogen bulbs?

 

Ford uses pulse width modulation (pwm) to power many items including headlights. PWM is more efficient and allows easy control of intensity. If you put an oscilloscope on the headlight signal it would be a square wave of some frequency above 100Hz.

Measuring PWM with a DC voltmeter will show the average voltage based on the peak height and the wave and frequency. I don't know if your high voltage is normal. If you are using Sylvania Silver Star type bulbs they have a shorter lifetime than regular halogens. Since headlights should be designed to operate at 14.5 volts, I would be surprised if 15.5 volts shortens their lifetime noticeably.