Easy replacement or wiring issue?

[Robbabob]

View attachment 31393

Drivers Side Taillight assembly. The bulb life span is way too short. Upon careful inspection, you see burned black plastic.

Can I assume I just need to replace the taillight unit, or will I have to get out the multi-meter and find a short? I am fearing the latter, as why would the thing burn up if not for a wiring issue?

Thanks in advance.

 

[christo829]

Mine did the same thing, just perhaps a little less black. I replaced the whole assembly, and so far,
no issues. When I first had issues with the original one, I discovered that there were two different bulbs installed, so
there may have been a resistance problem, or, more likely, the contacts got spread just enough to
create more resistance or slight arcing, heating the connection and melting the plastic.

Good Luck!

Chris

 

[The_Roadie]

The issue is entirely contained in the PCB assembly (aftermarket cheap replacements available at any parts store) and the lamp. You might shine up the lamp wires with sandpaper, and when you plug it in, plug it in and out ten times to clean up any oxidation in the socket that comes from storage. No need to trace or troubleshoot anything in the vehicle.

A short somewhere will almost always blow a fuse, not cause a lamp to overheat in its socket.

And as Chris points out, make sure you have the proper part number lamp installed and not one that looks the same but has more candlepower and draws more current to cause the melting. Goofball former owners have been known to install lamps without looking at the part numbers.

 

[kkoether]

The issue is entirely contained in the PCB assembly (aftermarket cheap replacements available at any parts store) and the lamp. You might shine up the lamp wires with sandpaper, and when you plug it in, plug it in and out ten times to clean up any oxidation in the socket that comes from storage. No need to trace or troubleshoot anything in the vehicle.

A short somewhere will almost always blow a fuse, not cause a lamp to overheat in its socket.

And as Chris points out, make sure you have the proper part number lamp installed and not one that looks the same but has more candlepower and draws more current to cause the melting. Goofball former owners have been known to install lamps without looking at the part numbers.

Also any kind of loose / bad connection can cause excessive current draw and cause enough heat to melt plastic. I just went through this on our microwave oven. A loose spade connection to a thermostat overheated due to excessive current draw and melted the plastic housing around it and ruined the thermostat. $9.00 for the thermostat and replacing the bad spade lug and the oven is working like new. Corroded pins in sockets and or on bulbs can do this.

 

[tbyoda]

Another reason is no dielectric bulb grease.

 

[blazinlow89]

Could this be caused by using a non SRCK bulb in the top socket. I don't know honestly just wondering if it could be a cause. My top one looked pretty bad but the other 2 were fine.

 

[CaptainXL]

Also any kind of loose / bad connection can cause excessive current draw and cause enough heat to melt plastic. I just went through this on our microwave oven. A loose spade connection to a thermostat overheated due to excessive current draw and melted the plastic housing around it and ruined the thermostat. $9.00 for the thermostat and replacing the bad spade lug and the oven is working like new. Corroded pins in sockets and or on bulbs can do this.

I think this is a common misconception. Excessive current is due to decreased resistance. I=V/R. As resistance increases current drops. Melted connectors are the end result of conductors exceeding their amperage capacity and getting too hot thus melting their insulators. Contact junctions between connectors happen to be the weakest link and overheat first. If the problem was just loose connectors then this would be a no foul condition as the only condition this would present is an increase in resistance.

 

[kickass audio]

The turn signal is not SRCK, it is a normal bulb. The running light and stop light are srck (I hate you GM for doing that). Halogen bulbs care less whether its a srck or traditional bulb because I put my lights and swapped them with the turn signals and put it on another vehicle that was not CK style and it worked just the same. I think the only time srck has any play is if you go for led bulbs like me. I blew the fuse on my truck when I threw normal led bulbs in there instead of CK style. And the weird thing is the running lamp in the back tail lights on mine is CK style but when I put in my CK led bulbs it doesnt illuminate no matter which way the polarity is. So I have all led's in my truck but the 2 running lights on the back because they wouldn't work no matter what I did. I don't even see the point of CK over normal bulbs but then again I can't speak stupid like the GM engineers can.

 

[kkoether]

I think this is a common misconception. Excessive current is due to decreased resistance. I=V/R. As resistance increases current drops. Melted connectors are the end result of conductors exceeding their amperage capacity and getting too hot thus melting their insulators. Contact junctions between connectors happen to be the weakest link and overheat first. If the problem was just loose connectors then this would be a no foul condition as the only condition this would present is an increase in resistance.

Perhaps I oversimplified it. Loose connections when vibrated will cause arcing which draws more current which causes heat and melts things. I see it a lot fixing machine tools. Vehicles see a lot of vibration also. Sitting still is a lot different than going down the road.

 

[CaptainXL]

Perhaps I oversimplified it. Loose connections when vibrated will cause arcing which draws more current which causes heat and melts things.

Right but we arent concerned with loads imposed by motors along with arcing. The entire circuit is fudged. Basically at the end of the day what we have here is a controlled short. The socket gets shorted and the bulbs burn out. Seems logical.

 

[The_Roadie]

I'm amused by all the speculation. Low voltage DC circuits don't involve inductive spikes on lamp wiring, although relay coil drive circuits can. Will write an essay when I get a bit more time.

 

[tbyoda]

I agree with last post, another thing that causes the connect to heat is a term in election industry called point contact. Basically the cross section of the contact has a too small of gauge to handle the current going through it. Just like to small of gauge of wire can't handle more current than it is rated for. I post the below pictures for example. These bulbs are our turn signals in the TB. As you can see the connection point on the bulb are round on flat point in the connector. Why you ask easy to mass produce. If the bulb had flat leads also like the plug this would not be a issue. Not to get to technical but this basically comes down to the smaller cross connect point = higher resistant or less conductive. If you are skeptical read the Wikipedia link.

http://en.wikipedia.org/wiki/Electrical_resistance_and_conductance

 

[tbyoda]

Low voltage DC circuits don't involve inductive spikes on lamp wiring, although relay coil drive circuits can.

Hmm interesting could have 10 or 20 (guessing) time the current for milliseconds but over time during blinking fires the connection.

 

[CaptainXL]

I agree with last post, another thing that causes the connect to heat is a term in election industry called point contact. Basically the cross section of the contact has a too small of gauge to handle the current going through it.

Essentially what I was saying. But lets see what Mr. Wizard..err Shelton has to say about it. Lol.

 

[Robbabob]

Rather entertained after being relieved with the replacement answer.

Glad the replacement answer wasn't at the end!

 

[kkoether]

It's been a while since I dug into this stuff. School was 34 years ago and I don't often stray into theory anymore. My job doesn't require me to use ohm's law and joule's law on a regular basis it just requires me to understand their principles.

Joule's Law for Direct current

The most general and fundamental formula for Joule heating is:
P=VI
where
P is the power (energy per unit time) converted from electrical energy to thermal energy,
I is the current traveling through the resistor or other element,
V is the voltage drop across the element.

Assuming a 2.1A draw on a 3157 bulb at 12 vdc. A .5 vdc voltage drop across a bad connection will cause 1.05 watts of heat dissipation. This is how bad connections produce heat and melt things in technical terms.

As I said I see this quite often in machine tools. Todays modern CNC machine is a lot more than just relays and motors. I work with 5 vdc all the way up to 480 vac 3 phase.