T1N tail light issue

My 2002 ex-FedEx van (extra long wheelbase) has not had proper tail light operation since I bought it. Only the left brake light worked, (and associated tail/turn light operation) and no license tag lights were present.

I'm sure there were several mechanics over the years, who attempted to fix various wiring issues, as there were butt-connectors all over the place. While I'm there, if you pay the extra money to purchase any connectors which include heat shrink material, please spend the time to use a heat gun on said connector. It will hold better and last longer. Many of the connectors fell off the wires as I was unwrapping the electrical tape. While replacing as many butt-connectors as I thought needed it, I noticed after market wire was added here-and-there, in an effort to either replace sections of bad wire, or to splice into good circuits to "fix" another circuit.

I cleaned the ground points at the front of the vehicle, under the seat and at the extreme rear.

The connector at the tail light assembly is held tight by a tie-wrap, after spraying both sides with electronic cleaner.
I contacted a Mercedes dealer about the connector and he's claiming only three dealers in the US carry the plastic piece, and no one has the pins on this side of the pond. When he verifies the connector I'll post the part numbers.

Here's what I have now. Left tail lights, turn signal and brake light works properly.

The right side remains a problem.

With no lights or turn signals on, brake light operates “normally” but dimmer than the left side.
Brake still on, put headlights on; brake bulb dims and turn signal bulb is brighter.
Brake still on, headlights on, put turn right turn signal on; turn signal bulb flashes, but so do both back up lamps (right and left).

Are there any spark chasers out there with a better idea of what is going wrong with this?

I'm assuming one of the previous guys either combined power wires or grounds in the wrong spot, but I'm growing old figuring this one out.

It does sound like the lamps are searching for a ground path, back-feeding and lighting other circuits.
My 2004 has a ground lug in the rear fender cavity for the lamp boards.
Perhaps someone along the line has removed/corrupted your van’s tail area grounds?

-dave

Did you try swapping circuit boards? Will tell you if it's a problem with the board or wiring. Boards are (on 2005) identical.

Vic/AquaPuttana found that some of the solder joints on the tail light circuit board itself had fatigued/failed.
Also that some of the metal bars had shifted position and short-circuited between themselves.

Reflowing the solder, adding bridging wires and occasional bits of insulation fix them.





--dick

If you have a mess back there you might consider a complete harness replacement for the taillights.
Million mile sprinter came to my rescue.

https://www.millionmilesprinter.com/shop

https://sprinter-source.com/forum/showthread.php?t=67781&highlight=porcupine


bill in tomahawk

The right-side board is an aftermarket replacement. The old unit had yellow paint marker on it, like it came from a junk yard, so it appears this has been an issue before I bought the van.

Here's the fix so far. Some time in the past, a mechanic spliced into the the left-side tail light at the marker light wire and ran a wire up the body column across the back-door opening and back down the right-side body column, where it was spliced into the right-side connector. Figuring there must have been a problem with the right side wire, I traced it back up to just above the axle, where there were multiple wires "repaired" with butt connectors. I replaced a couple of the butt connectors and sections of wire, then removed the previously made jumper.

The other obvious problem, which I missed, was that the ground wire on the right-side connector had been pulled out of the connector. The fix that had been tried was to create a new local ground using a body bolt nearby (there's a handle on the side to aid in pulling yourself up) and then wrapping the loose end around the ground buss on the board. This wire was loose was not creating a ground. In fact I must have pulled it off the board when I replaced the board and never tried to replace the ground. Since I don't have a kit to fix the pin and wire in the connector (still on order from a Mercedes dealer) I decided to re-use the nearby ground option. I happen to have a micro-spot welder, and I was able to put a thin nickel strip on the ground buss, then solder the wire to that strip for a better connection.

By the way, in case you are in search of these connectors. The original was a five pin configuration. The board includes six pins, one not being used on this model. The replacement connector has six pins, so when it arrives I'll have to remember to leave one blank/empty. I'll post the part numbers once they arrive and I can verify use.