Understanding how "LAMP OUT" indicator works ?

[verk]

Hi TDR folks. I just replaced my original discolored headlight assemblies when a low-beam headlight filament finally failed after 19+ years of service! LEDs may last longer, but still impressive. After I replaced these headlight assemblies I started to experience "LAMP OUT" flickers on instrument cluster display along with erratic relay control timing that matches the flickers. This occurs ONLY when using the turn signals and only when the headlamps are on. All bulbs are incandescent. Before I go starting to troubleshoot this I wonder if anybody knows how this monitored circuit works ? From the manual it seems FCM is responsible for generation of "LAMP OUT" messages which are sent over the PCI bus and received by instrument cluster. The manual seems to say that there is a turn on "LAMP OUT" and a turn off "LAMP OUT" message so I think this behavior shouldn't be happening multiple times per second as it is. So the monitoring of these circuits is within FCM and is based on current threshold for all light circuits ? In other words, below a specified amount of current and the FCM knows that one or more of the light loads isn't working ? The bulbs look as bright as intended so I don't think I'm dealing with a current problem, but that this problem started with new assemblies is suspicious. Perhaps this flickering behavior or "LAMP OUT" is a dead giveaway of a bad FCM ?

Thanks for insights. Sven

 

[Ozymandias]

It is resistance that is used for this.
I just replaced mine a couple months ago. During research I stumbled over several reviews where people mentioned to see "lamp out" warnings after installing the new assemblys. In the end it boils down to the point that the aftermarket front turn signal sockets are sketchy. Every single one replaced them with the old factory ones, problem solved.
I hope you still have them.

 

[Darkbloodmon]

I replaced my OEM 03 housings with TYC units, but I bought the turn signal lamp sockets from Mopar. When I was reading into my housing replacement I stumbled upon a few write ups warning of the lamp out messages which was linked to the turn signal sockets. I don't know what kind of pixy dust Mopar uses that everyone else can't but I've had no issues with my housings when they were fitted with Mopar sockets.

 

[verk]

Looks like they mixed up park and turn within each connector. Subtle, but I guess the 0.5+ ohm difference in filament resistance (cold) of distinct functions is enough to throw off monitoring circuit.

 

[verk]

Thanks for replies. Already removed the mux switch to check on resistance of turn function. Probably would have taken a long time to figure this out had somebody not responded. I think this forum and forums in general have saved me countless hours.

 

[verk]

Can anybody identify the make of this connector as used in this front park/turn socket ?

 

[Tuesdak]

Lamp out uses a low current and about 7V measured with the lamp in question removed. Not enough current to light the filament up. Not enough voltage and current to blast through corrosion or a loose connection. There is no "latching" for a moment to keep the indicator "on" when bumps shake a problem turn signal lamp in the bad socket.

It's a design that simply falls short as they missed dealing with a intermittent bad connection that the full 12V can blast through. The condition comes and goes faster than the Lamp Out chime can finish. And as they all light up: what lamp is bad again?

On inspection you may find just a small black dot on the trouble spot lamp connector wire. This matches the bad connection spot in the lamp socket.

IMO this is one of the few things you load and fire the parts cannon at. Not only that but WARRANTY the new lamps you got. Or just toss them as one is now bad at it's connector: The bad socket connection may have damaged the new bulb connection by an electric arc. Shoving a bad bulb in a new socket ruins it. Can you clean it and maybe: been there done that and repair quickly failed.

Loading the cannon: Replace the turn signal sockets, headlamp sockets, taillight boards and EVERY SINGLE EXTERIOR LIGHT BULB!

The lamp is fine you say ... Lights up you say. It's NOT FINE!!! The connector on the lamp and socket are damaged quickly, if not instantly, by an arc.

I would also inspect the 3rd brake lamp lens and board. I replaced mine, lamps and all, due to lens melting. IDK if this assembly is part of the lamp out or not, but, I wasn't taking chances.

You can attempt to be cheap and ignore the Parts Cannon advice above, however, you will have to hunt down the bad connection when it's acting up that takes time and the damn ding-ding-ding randomly going NUTS. Frugal is literally MOPAR sockets and everything as above: problem solved.

After the above it can be problems with connectors to the sockets - not fun.

 

[Bar9]

Just to add my most recent experience. Replaced both rear tail lamp housings and almost right away started seeing lighting issues. Only reason I noticed was due to my running lights dimly illuminating when braking on my horse trailer. After hours of messing with my 7 Pin and Trailer thinking the issue was between them, I noticed when my GF was hitting the brakes the park lights were coming on in my headlights very dimly. More hours messing around, lucked out and swapped the aftermarket tail light sockets and the problem was resolved. So it was a resistance issue for me, highly recommend sticking with OEM connections and sockets.