I like to get my information first-hand since I’ve seen some impressively glaring omissions (or worse) in supposed-to-be-reliable sources. Not that I totally ignore that; I reconcile all my sources and try to make sense of it all.

I’ve been trying to get a handle on when the W126 range split. My 1984 W126 4-door is significantly different (as to a great many little things) from my 1989 W126 4-door, and I’ve been trying to find the exact cut-off when the “significantly revised” range was introduced.

At this point, my conclusions match what Wikipedia implies: the 1986 model year was the first of the revised models.

On my 1991 300SE, I can make the driver side front window slide up or down by putting my palms on either side of the glass and pushing up or down. Not that I need to do much pushing down … gravity does that gradually, as I drive.

Today, I analyzed a parts donor car, so as to learn more about likely causes of the problem, and how to get access to the relevant parts.

The first step was to open the door. No problem there.

I removed the seat control switches. I pulled the little black plastic miniature-seat pieces away from the door to remove them. Then, I pried away the plastic cover just below that. One side has three fairly flexible tabs, and the other side has one large tab. I broke one of the tabs on one side.  With the cover out of the way, two small yellow Phillips screws become visible, and with them removed, the switch base could be accessed and removed. I also pulled the wiring plug away from each switch.

I removed the door handle. With the window switch base out of the way, a large yellow Phillips screw becomes visible. I removed that, and two similar screws in recesses in the door handle. With the three screws removed, the door handle can be lifted free.

I removed the door lock knob, by turning it counter-clockwise and then lifting it away.

I pulled the door trim away from the metal of the door; I own a tool for that but I hadn’t brought it along. Girl arm muscles worked well enough, as did digging in my nails around the edges to pry the panel away.

I removed several (non-identical) 10mm bolts and one or two 10mm nutes, and the window winder mechanism came loose. I chased its wires. Two of them can be loosened by removing two Phillips screws, but there’s another three-wire harness for which I couldn’t find an easy disconnect point, so I cut the wires.

I could maneuver the mechanism downward but not free of the two metal guides at the bottom of the window glass, until I removed a 10mm bolt that was clamping the mechanism to the guide.

I’m not sure that I needed to get the window out, or remove parts in order to get the window out, but I did anyway.

The two vertical guides for the glass are non-detachable as far as I can tell.

On my 1991 300SE, I can make any either of the rear windows slide up or down by putting my palms on either side of the glass and pushing up or down. Not that I need to do much pushing down … gravity does that gradually, as I drive.

Today, I analyzed a parts donor car, so as to learn more about likely causes of the problem, and how to get access to the relevant parts.

The first step was to open the door. No problem there.

I removed the door switches. The donor car was a 560 SE or SEL, so the door switches have more features than on my humble 300SE, which doesn’t offer heated or adjustable rear seats.  Even so, I pried the switch surround off with a flat screwdriver. One side has three fairly flexible tabs, and the other side has one large tab. I broke one tab on each side.  With the switch surround out of the way, the switches could be accessed and removed, by pressing their catches inward with a flat screwdriver, and pulling the wiring plug away from each switch. I bought the two window switches; I plan to see if they’re the same as in the center console. If so, they’re probably less-worn.

I removed the door handle. With the window switches out of the way, a large yellow Phillips screw becomes visible. I removed that, and two similar screws in recesses in the door handle. With the three screws removed, the door handle can be lifted free.

I removed the door lock knob, by turning it counter-clockwise and then lifting it away.

I pulled the door trim away from the metal of the door; I own a tool for that but I hadn’t brought it along. Girl arm muscles worked well enough, as did digging in my nails around the edges to pry the panel away.

I removed several (non-identical) 10mm bolts and one or two 10mm nutes, and the window winder mechanism came loose. I chased its wires but couldn’t find an easy disconnect point, so I cut the wires.

I could maneuver the mechanism downward and then free of the single metal guide at the bottom of the window glass.

I’m not sure that I needed to get the window out, or remove parts in order to get the window out, but I did anyway.

I used a flat screwdriver to lift the flat, black horizontal door weatherstripping rubber that runs alongside the bottom of the door-and-window opening, on the inside of the car.

I used a flat screwdriver to lift the chromed horizontal door weatherstripping rubber that runs alongside the bottom of the door-and-window opening, on the outside of the car.

I pulled the window rubber surrounding the glass out of the car.

The rear window glass has two pieces: a rectangular piece and a somewhat triangular piece, to the rear of that. Separating them is a vertical metal pillar, part of which is painted body color. With the door rubber removed, a small Phillips screw is visible at the top of the pillar.  After that screw has been removed, the pillar can be maneuvered free and out.

I recently bought a 1989 300SE that had been sitting for long enough that the fuel tank was all gunked up. I removed the tank, washed it out with some impressive solvent, then paid someone a few bucks to pressure-wash it inside. Back into the car it went, and it’s now living happily there, and the car starts and runs.

However, in the process of taking the tank out and putting it in, I damaged the fuel level sending unit at the top of the tank.  It’s still out of the car. Today, I know exactly how much fuel is in the tank because I personally poured in a couple of gallons, but once I start driving the car, it’d be nice to be able to rely on the fuel gauge.  Besides, a big, gaping hole atop the fuel tank probably will make anything in the trunk (and maybe the cabin too) smell like fuel.

Now that the car starts, I’m focusing on the sending unit. I spent some time on a donor car today, trying to get a sending unit removed. I failed as to the sending unit itself, because I needed to rotate the entire unit, and for that I needed either an adjustable wrench or a massive socket (more than 40mm, I’m guessing) or a huge wrench — none of which I’d brought along.

However, I learned a lot, and I did get the wiring, which is part of the problem; I’d crushed the black plug at the top.

I’d feared that I’d have to remove the entire fuel tank to work on the sending unit, but, today I learned that I don’t have to do so. After I remove the rear seat back, I can see a shallow, black, plastic plug, and when that’s been pried up and removed, the top of the sending unit is easily accessible.

I love how logically these cars are designed!

Today I was cruising at (very approximately) 65 mph and 3500 rpm in top gear in my 1991 300SE. I decided to stomp on the accelerator, and the transmission downshifted and the rpm went up to 5000 or more, good. Zoom, off we went, fast — but I kept the pedal on the floor and then the transmission downshifted again … NOT good.

I saw the rpm needle swing high, way deep into the red-line; if not to 7000 rpm then darn close to it. The engine was surging too; presumably trying to limit the engine speed by doing so.

I backed off and drove normally, listening for obvious sounds of engine damage. It all sounded normal.

After a while, I tried the downshift again, but this time I used the shift lever. Starting today, that has become my preferred way of downshifting.

I’m worried about engine damage. I plan to do a compression test soon, to check.

Two of the three windows on my 1991 300SE no longer open or close electrically, and I can make any one of these windows slide up or down by putting my palms on either side of the glass and pushing up or down. Not that I need to do much pushing down … gravity does that gradually, as I drive. I haven’t found out how to get a window up if it’s ever all the way down. I might not like the answer.

I’m getting pretty tired of the hassle. Also, drive-through ordering is a pain due to a window that I can’t open while I’m sitting in the car.

So, today, I went to an auto glass shop whose owners I like and trust, and whose prices are typically low. Their price: $150 per fix per door, $450 total. Whoa! That would be with new parts; they don’t have any used parts on hand. Wow! Good thing I’m in the used-parts business.

So one more item on my task list is to immerse myself into the world of W126 window winders….

I have mangled many W126 trunk lid badges while trying to gently remove them from cars at junkyards. I finally gave up on it and I delegated the work to my competent assistant. She worked a serrated bread knife gently underneath the chromed plastic, and gently carved and leveraged the badge from the trunk lid. Success!

Soon my 560 SEC will not longer have a badge with the “C” broken off so that it reads “560 SE.” Better …

Part number 201 821 00 47 belongs to the relay for the indicator lights, hazard lights, wipers, etc. for the W126 Series (1986, 1987, 1988, 1989, 1990, 1991) Mercedes-Benz 560 SEC.

We guarantee that this part will fit this model.

We are offering this part (number 201 821 00 47) used and guaranteed, for $40.

• Please add $15 for shipping to anywhere in the US.
• Nevada residents, please add 30 cents (which is 7.6%) for sales tax.

Our parts are used but original Mercedes-Benz quality, guaranteed to fit and work, otherwise (your choice):

• We replace it at no charge or
• We refund your money and the shipping costs to you and back to us.

Below is a little write-up that we hope you will enjoy — one more reason to be enthused about keeping your Mercedes-Benz on the road. You could buy the parts from a vendor who doesn’t understand or care about Mercedes-Benz cars, or you could buy from enthusiasts like us. We hope you choose us!

To remove the part, you normally don’t need any tools (how nice is that?) First, look at the above picture to see how the pins look. Then grasp the module firmly but gently, and slowly wiggle the module back and forth, to “walk” the little pins loose. Then, lift up the module and move it up and away from the general area.

If it’s stuck, resist the temptation to yank it hard. Either keep patiently wiggling it, or work a screwdriver or dull knife under the edge of the relay to pry it up.

To install the replacement, make sure the pins are aligned correctly, and then gently place the module in position and push down until you feel that it is seated.

This should help dispel the myth about Mercedes-Benz vehicles being overly complex. Yes, the internal functionality is complex, and necessarily so, but Mercedes-Benz has made that nicely modularized, and the part is so exceedingly easy to remove and to install that you require no specialized tools or knowledge. That’s about as simple and easy as something like this can be.

In software design, modularization is good. The same is often true for electrical circuit design. Mercedes-Benz seems to be exemplary. Rather than spreading the complexities of the turn signals, hazards, wipers, rear defroster and trailer hook-up across a massively complex wiring harness, Mercedes-Benz consolidated it into one nice module that’s easy to remove and to install. It’s typically in the engine compartment on the driver’s side, close to the firewall, or inside the (nicely protected) fuse box. The functionality and design of this particular module have been so universally applicable that it was used in many models in the W126 series, the 1979 – 1991 S class, over many years.

This standardization reduces the production costs as well as inventory costs for the factory and repair shops.

This means the money for purchasing and servicing your Mercedes-Benz goes more to aspects that add value and less to inefficiencies.