Problem found and fixed!

Key on, battery light comes on nice and bright.

Right after the engine starts all three lights (battery, brake wear, brake) go off just as they should. Here are my nice functioning lights:

http://www.peachparts.com/shopforum/...1&d=1480489818

Here is what all I ended up doing:

- removed the big aluminum box that is in the way of accessing the underside of the fuse box; there is a single 10mm bolt that holds it in place.

- removed the nut holding the fuse box in the engine compartment

- loosened or cut some of the plastic ziplock-like ties that attach the cables to parts of the frame

- disconnected the wires at fuse #12, first the "fused" ones, then I was able to access the terminal where blue/red meets with two red/black.

Here is the picture of that terminal:

http://www.peachparts.com/shopforum/...1&d=1480490241

Notice how the blue/red wire strands are just loose there? It turns out that those are the only strands that are exposed, and they were not soldered to anything. They were merely touching the rest of the connector.

When I disassembled and de-soldered the connector, the fact that the blue/red wire wasnt soldered became even more evident:

http://www.peachparts.com/shopforum/...1&d=1480490266

See the solder on the fat red/black and the skinny red/black wires but none on the red/blue:

http://www.peachparts.com/shopforum/...1&d=1480490716

Here is the reassembled terminal:

http://www.peachparts.com/shopforum/...1&d=1480490793

I was then able to test the continuity between the reassembled terminal and pin 6 of the instrument cluster connector, and measured minimal resistance.

I then reassembled everything and tested. Yay!

THANK YOU ALL FOR ALL YOUR HELP especially funola and Diseasel300!

Congratulations! Few things are more rewarding than fixing an irritating electrical gremlin! I know exactly the feeling you had, I felt it when I was able to turn on my headlights and not blow 3 fuses in my fusebox! I chased that damn fault for 3 months before I found it.

Good it's finally fixed! Does it look like that terminal was made that way from the factory? Did it have heat shrink over it? Somebody botched that connection real bad. The blue/red wire, besides having only 3 strands, should have been crimped and soldered with all strands instead of just laying there with 3 strands. I am sure the charge indicator worked when it left the factory. Over time, oxidation of the terminal and the copper strands made that connection to have higher resistance (not capacitance) to the point the charge indicator stopped working.

It had a black shrink wrap over it that was pretty thick and seemed to be the save as on the other terminal...

The crimping job looked good and the solder was neat and factory looking. It looked like the blue/red wire somehow didn't make it all the way into the "crimping/soldering machine" and remained outside of the terminal. It may have been the crimping device that then mauled most of the strands away from it, but I'm just speculating now...

I made sure I heated the $&@$ out of it with my solder gun, then put my own heat shrink insulation over it.

I suspect it has worked all these years on just the couple strands that made the electrical connection, then perhaps a strand or two or three broke over those years until there was not enough connection left leading to the eventual complete failure.

Sounds like it came botched from the factory. Being an 83, don't think robots were used back then so it was hand made. If the missing copper strands were not inside the heat shrink, then the insulation was stripped too deep leaving only 3 strands. That German worker must have drank too much beer.

Is your cluster 15 pin or 14? Did you have battery problems with the charge indicator broken?

There are 14 pins, pin 9, which must have been the buzzer on other cars, is missing.

I did not have battery problems but Looking at the schematic, the battery wear indicator must have provided the current needed to excite the alternator... ?

I didn't realize this until looking at the wiring diagrams over the last few days that this may be true. We know the charge indicator lamp provides excitation to the alternator. In addition to the charge indicator, the brake wear indicator (battery wear indicator was a typo), there is also the brake warning and low fuel warning lamps, each in series with a diode and an 18 ohm resistor, that also provides excitation to the alternator. Or it could be that the alternator self excites when revved above a certain rpm and no external excitation is necessary.

If anyone wants to test these theories:

1. Install a cig lighter volt meter, remove the charge indicator lamp, go for a drive and observe the voltages. Should be between 13 V to 14.4 V if it is charging.

2. Remove the brake wear, brake warning and low fuel bulbs and check voltages again.

If it still charges after 1 & 2, the lamps are not necessary for (your) alternator to charge the battery. Their main function is to provide warnings for faults in the alternator, low fuel, parking brake engagement, brake wear, brake fluid levels.

I think I will try that. I can't take it for a drive really yet because all my door lock strikers are shot and the new ones won't be here till Monday though...

It'd be interesting to see the results. What happened to your door strikers? I thought nothing ever goes wrong with them.

When you have the cluster out, take and post pics of both sides the module with the circular connector.

Based on the schematic, there should be enough contribution from the warning module circuit and Brake Wear indicator to help flash the alternator even if the main warning light is out. If the engine is revved, I'd expect the residual voltage to be high enough to self-excite anyway regardless if the idiot lights are working. The teaser circuit is just there to "flash" the field and get the alternator working immediately at idle and to warn the driver if the alternator quits producing.

The door strikers can have issues. Particularly if the rubber bit goes missing on the leading edge, sometimes the door will just refuse to latch or require a stunningly hard slam to get it to stay closed. I had one wear like this on the SDL and replacing the striker solved the issue.

This is correct. The odd connection of the brake indicators and similar warning lights is a peculiarity of Mercedes dash pods. They ground through the field just as the alternator warning light does in order to test the bulb during start-up. As with the alternator light itself, the bulb goes out when there's power on both leads. Any of the bulbs is sufficient to supply excitation current, so you may be ok even if the alternator bulb is bad. The diodes are there to prevent the alternator from shorting out in the event you have an actual brake problem...when this happens, the brake indicator becomes grounded through the wear sensor to the brake rotor. Without the diode, this would ground the D+ connection in the alternator, causing undesirable smoke release.

I would say with near certainty that the wiring you repaired was NOT factory. There's absolutely no need for solder, as long as the connector is properly crimped. Soldered connectors are usually a tell-tale indicator of shade tree "improvements".

While I was working on the cluster, the driver side door stopped closing. I tried the passenger door, opened and closed it a few times, and it stopped closing.

I started looking at the rear passenger door, poking around that plastic piece on the striker that makes the lock "lock", and broke that.

So I have three strikes that are broken. All are missing the plastic pieces that help "flip" the lock into locked position.

Some people have reported that their doors work without them. Once of mine does, two don't. I ordered four new strikers and going to replace them all.

That plastic gets brittle and breaks off after 30 years.

Are you 100% sure there was no soldering done on those connectors at factory? Because it just didn't look like anyone messed in there... it looked like too much trouble to get in there, and the factory plastic zip lock things were intact, and without undoing them one couldn't really get to the back side of the fuse box...