I had this same issue, especially on bumpy roads but also on smooth surfaces. All the lamps were working, and the bulbs all looked good, but when I pulled all six out; there was one lamp that the plastic base had melted over the wire, changing the electric current flow, and thus causing the “lamp out” indicator light to illuminate and “ding” sporadically. Sometimes it would “ding” but the indicator light wouldn’t illuminate. Replacing that lamp in the tail light for $5 fixed the problem!

 

The Front Control Module FMC attaches to the fuse box , this controls the low an high beams and all lights and prone to issues, I have to shim mine between fuse box which it plugs in to , and this keeps my low beam working on passenger side which is the one that was out for me on low beam , sometimes I have to push on t but it works for the most part as you cannot by new only used I found maybe someone else knows different ,,others have wired there low beams to marker lights but the lamp out light stays on when this is done

 

I have a 03 ram 1500.
All the lights worked but that light came on. Couple days later my passenger turn signal light went out. And it fixed it.

but not the “lamp out” is still showing. I’ll just disconnect the battery for couple minutes and see if that works.

 

04 Ramm 1500 SLT. My light out indicator only comes on when I have headlights on and use my turn signal or hazards. I know, it's no where near as annoying as some of you, but none the less, it is annoying at nighttime. All lights work and appear to be good. Anyone else with a similar situation and how did you get it to go away or what fixed it?

 

So I had same issue on a 2004 Ram I got from my friend. It was in an accident on fron driver's corner. Not long after repair, this would happen on both sides tuen signals only when parking lights were on. I replaced tear taillight boards as those were beat to hell, I thought that would fix but no. I checked grounds and ran fresh ground to paring lamp sockets as the ground wires were a bit green a good ways up, still not fixed. OK, removed IPM and FCM, tore down IPM into the separate layers of PCB and cleaned off some corrosion, fixed a short and epoxied it, still not fixed! Finally I just replaced the front turn signal sockets and all is good now! No more lamp out! I am trying to post this everywhere as I see not many people try replacing the front sockets because they look good upon inspection, but something inside goes wrong. Mine were the driver's side 12v was ever so slightly bleeding over between the 12v turn and the 12v parking pins, the passenger side was high resistance in the ground pin.