What's the latest on the headlight? I've had the same issue. At one point (actually a couple of times) I took TIPM off, cleaned contracts, and tweaked slightly the larger contacts. Both lights worked after that, for short while. Too many bumps or whatever and it is off again. Run with fog lights so I don't get a ticket.

 

Having this same trouble with my 2004 2500 diesel, driver side headlamp out, had all the wiring apart today, pulled all connectors out and checked all contacts. It started out intermittent and you could wiggle the PCM/FCM and it would come back on, now it won't come on at all. Tried the bulb from the pass side, it won't work either. Both bulbs work on pass side of truck. Checked wiring, only thing I see is where they tied the Hella Fog lamps into that feed to get the 12v feed for the switch/relay to run the fog lights. Fog lights don't work when the headlight doesn't work. I've checked with a meter, getting ~3-5 volts on both positive pins using the ground pin in the plug or going direct to the battery. When I connect the bulb back into the socket and test on the low beam wire (white/dark blue stripe) I get no voltage. Unplug the bulb and the ~3-5 volts is back. High beam works fine on both sides. No other issues aside from that. When I first bought this truck it had the same issue, took it back to the dealer I bought it from, they "replaced the TIPM" per the service manager at their shop. I know that my year doesn't have a TIPM, but does have the PCM/FCM assembly. Don't have the wiring diagrams but have been able to follow the basic wiring route, no issues on the wire itself. Any help would be appreciated, I've got it all torn apart still, now's the time to fix it. Thanks for the help.

 

The IPM has to get continuity in order to send a 12V signal to the headlight, which is why you get the 3-4 volts, Its "testing" to see if the bulb is burnt. sometimes your test light fill flash pirodically if testing at the connector. If you dont have a good bulb connected, the IPM wont get continuity, and wont send 12V. (its the stupid "LAMP OUT" system) then maybe if it is prolonged or something then IPM would require a reset.
Try disconecting both batteries + then touch the + to the negative post of a battery. this will release any memory in the IPM and COULD be a simple fix if the IPM needs to be "reset".
I experienced something similar to this while wiring a flatbed on a truck. I was experamenting and had the wrong wires hooked up so the "lamp out" light would flash and ding with the blinker...kinda funny but anoying. And then the blinker would quit working even with a new bulb. It would still blink in the cluster but not at the bulb. Id follow the above process and it would reset the IPM (FCM in the case of the rear wiring) and the blinker would work again if wired correctly.

 

Found a corroded pin on the FCM, cleaned it up and the headlight is working now. New trouble is that the truck died while driving it the other morning, pulled it back to the house with the trusty old first gen and it's sitting there dead in the yard. It will crank but won't start. Anyone know how to get the trouble codes out of it so I can see what the computer thinks is wrong with the truck? Thanks for the help, wish this thing was as simple as me and my old first gen.

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Update- just checked for codes, none in it, so I cranked it until it finally started, about 15 seconds. It ran ok, gave it some pedal and it bogged and died. Cranked it again, it started, about 10 seconds that time, let it idle, put the AC on, then took it for a test drive, it ran smooth, then went to give it some pedal, it bogged, then something cleared, it downshifted, and then proceeded to **** and get down the road, ran it a couple more hard pulls and another good pull with it at a 40 mph roll, and it seems fine, guess it just got some junk in the fuel line or it's almost time to change the fuel filter. Thanks for the help guys.

 

Update:
I went through and cleaned all the corrosion off the contacts and filled the plug end with dielectric grease and all has been well ever since. The fuel issue I had run into was that there was a bunch of junk in the fuel tank, killed another stock tank pump assembly. Have since gone to a FASS Titanium and 1/2" draw straw upgrade. Everything has gone really well with it. Have a new issue cropping up but troubleshooting it as we speak. Hope this was helpful for some, I know I've gotten tons of help on here, want to be able to pay it forward.