98 SL500 LED 3rd brake light isn't very bright
 

I fixed a broken wire in the hinge area of the trunk lid and got this light working.

The LED array sure isn't very bright. I'm sure that there isn't any grounding issue. The connector has its own ground, and I also removed the LED array unit from the car and tested it with a power supply.

All the LEDs work and appear even in intensity.

Is this the way these things were in that era before hi power LEDs?

daidnik,

I don't mean to hijack your thread, but I need to ask about how you fixed your third brake light. Mine is broken and I am told I need to resolder it. If you don't mind could you elighten me either here or by PM?

Thanks.

Wire breaks tend to occur in vicinity of the hinge
 

Troubleshooting is best handled by first removing the trunk lid cover panel. This isn't hard, but it is good to make a tool to pop the plastic fasteners out of the holes without breaking anything. I've made several of these out of some flat sheet steel about 0.030 thick or thereabouts. Get a rectangle about 2 inch wide x 4-5 inch length. Notch a roughly 1/4 inch square-ish cutout in the middle of one end of the narrow (2 inch)side. Round the exterior corners to make the tool reasonable friendly, give it a bend near the end in the long direction to make a kind of curved spatula and then you're ready to go. You can use this to slide the notch right up to the plastic fastener buttons and pop them loose without breaking the plastic holders on the trunk lid cover. You don't want that. Replacing the plastic buttons is easy and cheap, but I doubt that the plastic holders glued to the trunk lid cover are even available.

Anyway, with such a tool, you won't even break any of the buttons let alone the holders.

Once you get the cover off, you'll see the wire going over to the rubber guide on the right side of the trunk lid.

Finagle that rubber conduit piece out of the grommet hole in the trunk lid without tearing it; mine was a bit tight, but just be gentle and work it out of the hole. Similarly, remove the other rectangular end out of the trunk hinge going downwards.

Once you can see both ends of that rubber conduit piece exposed, you can work the wire IN/OUT on both ends. The two wires are in a sort of greasy black gauze sheath that seems twisted about the wires. You can untwist it a bit and see the wires. The Black w/ Red wire was the +12V line on mine and it was completely broken (obvious Open Ckt). The Brown Gnd line was also breaking.

I spliced in a some new wire pieces with heat shrink tubing and worked it into a slightly different position in that rubber hinge conduit piece, so it should be good for some number of years.

If the stranded wire they used would have had more strands, it would have been more resistant to this sort of fatigue. You'll see it's pretty stiff stuff.