I have a 2000 F-350 7.3 4x4 with 145k miles. I have owned it for a long time and it is bone stock. The drivers side headlight has been dim for a few months and I finally got around to trying to fix it. Below are some of the symptoms….any wisdom would be much appreciated.

I replaced both headlight bulbs knowing that probably wasn't it because the bulbs were 10+ years old anyway. No change.

Multimeter test….I thought the dim light might be a ground wire, but i tested the ground off the + terminal on the battery with the multimeter and it read the full 14.5V with the truck running. I then tested the low and high beam wires. Both read about 13.5 V with the truck running no matter if I grounded it through the ground wire, or - batt. terminal. I tested the passenger side low and high beam wires and they both read 14.5 V. To me this shows the dim light isn't getting the correct voltage.

With the headlights on, if I pull back the high beam lever to flash, the drivers headlight goes out completely (dim one).

With the headlights off, if I pull back the high beam lever to flash, the drivers headlight comes on but it is dim, just like with the headlights.

 

Measure for voltage drop across the ground connection from neg battery post to headlight spade lug and then later positive post etc,, for each headlight while under load.

Zero volts would be best, anything more than 2/10ths (0.2) or so is too much.

 

check and/or replace each of the fuses for the headlights. it isn't uncommon for a fuse to partially blow

there may still be enough fuse link for the light to work...barely, but not transfer full load

 

[QUOTE=Tedster9;14956841]Measure for voltage drop across the ground connection from neg battery post to headlight spade lug and then later positive post etc,, for each headlight while under load.

Zero volts would be best, anything more than 2/10ths (0.2) or so is too much.[. Was it your multi-purpose switch on your steering column I kind of really would like to know what your problem is because I've got a headlight that worked on high coming home about 300 miles and then after we worked on the front end of the truck now I don't have the passenger side headlight working only the driver side and it's got high beam and low beam on the driver side I'm just kind of baffled and what's wrong with the left side I have pulled a meter on it and I've got power when the trucks running but on the dark green wire they're showing no power it did not running just baffles me for any help with repreciate it

 

Had this happen...put up with it for years...on the wife's 00 Excursion on the passenger side headlight. The wiring to the socket that plugs into the headlight assembly is what my problem was. The wiring is too small and will heat up and start creating havoc. When we would first turn on the headlights I always had to pop the hood and jiggle the wiring at the socket just right to get it to stay on as it was always really dim. I decided to upgrade the headlights in my 00 F350 to the 05-07 Harley style and had to change the pigtail plug in sockets as they are different. I took those from my F350 and installed them on the Excursion which solved the problem. However, once I inspected them I could see where the plastic plug in was melted where it plugs into the blades of the bulb thus causing the issue. It's been a couple years now and no more issues...though I did install LED bulbs in both trucks given they are much brighter and whiter light, but also use less energy than the original halogen bulbs which is easier on the wiring...