Question for the electricians out there regrading melting SLK tail lights.

[Chris]

I recently had an opportunity to discuss the melting SLK tail light issue with an owner who had both tail light housings replaced. Note this was on a 2002 model so I still think this may be an issue with the newer SLKs.

He showed me his old tail light housings. Stangely enough only one was damaged, but the dealer replaced both housings under warranty. What I observed was a light browning of the blue brake light bulb holder. The holder was not melted, but it obviouly was exposed to a lot of heat which caused the discoloration. I did not notice any corrosion or melting of the metal contact points. The heat from the bulb holder caused the hole in the housing which takes the brake light bulb holder to melt and deform which made it difficult to remove from the housing. The heat also resulted in bulb failure and the failure of the brake light to work even after the bulb was replaced. However all other lights in the assembly continued to function.

I find it strange that only one light assembly had the problem. I wonder if the wattage on all the larger bulbs (that is all bulbs except the actual tail light bulb) generates too much heat if used continuously (possibly only in warmer climates or possibly only on those cars with automatics since I assume these owners have to keep their foot on the brake when stopped). The tail light assembly design looks fairly simple, but I do wonder if there is a design flaw. Could some kind of arcing cause the problem, and will Oxy-Gard prevent the problem?

[AA430]

I wonder if the wattage on all the larger bulbs (that is all bulbs except the actual tail light bulb) generates too much heat if used continuously (possibly only in warmer climates or possibly only on those cars with automatics since I assume these owners have to keep their foot on the brake when stopped).

Heat from the other bulbs causing melted plastic is highly unlikely. If it was a design flaw, then you would see more instances of this occuring.

If it was a design flaw, then both housings would have melted at around the same time.

It could be material flaw, in which case, sounds like a low probability (i.e. the guy was "lucky").

If one argues that the bulb short-circuited, then the fuse should have burned first before a large amount of current can flow through and start essentially start a fire. --- Fuses can go bad also.

[Bruce R.]

The bulb sockets make contact with the stamped circuit "wires" in the tail light assembly. That contact if small enough can generate a terrific amount of heat. That heat has caused welding of the contacts, melting of scokets, and other damage.
Since all of the components are stamped, there is an excellent chance that a small feather of smeared rather then cut metal can be left on the very edges of the various cut parts, it's these "feathers" that can cause the problem.
The design should have been better. The contact should be in the bottom of "U" shaped area of the socket contact fingers, not the "feathers" of the metal edges.
There is a cure, but it requires effort on "our" part. You must remove the Brake Light socket and clean up the contact points with some very fine sandpaper, also clean up the contact surface of the stamped curcuits with a pencil eraser. You can then reassemble with Oxy-Gard as Brian has used, or you can use heat sink grease from Radio Shack or similar, both will work.
The trick, if there is one is to get GOOD contact between the electrical components.
Hope that helps, it did for me. [:o)]

[Brian_R170]

My service advisor said that another reason the taillamps go bad is because there isn't enough tension to hold the contacts tight against each other. Obviously, you can fix that by bending the contacts slightly before installing the socket. Of course, you still have to do it before you have a problem.

[AA430]

It doesn't sound like a design flaw but rather, to me, a production/manufacturing yield issue with the stamped contacts.

Regardless, you're right, a stray piece of metal from the manufacturing process would cause a similar problem.

Given this, it IS a design issue if this failure mode isn't accounted for by the designers.