I checked the 201 chassis manual and 124 CDs, but it's not mentioned - group 54 where the part is illustrated.

It's under the center console at the back of the linkage frame. No visible fasterners that I can see, but visibility is limited and access is tight. I figure it must snap in.

What's driving me nuts is that fuse 9 is okay and other functions on that circuit operate and there is power at the harness connecter with the ignition on. If I short the two leads on the harness connector, the backup lights illuminate.

The switch shows continuity when the shift lever is moved to the reverse position or if I manually activate the plunger, and it's open when the shifter is out of reverse, but when I connect the harness to the switch and shift to reverse or push the plunger down manually the backup lights don't illuminate.

I removed the two female terminals from the harness connector and fitted them to the switch pins. They weren't that snug so I tweeked them for a snug fit and still no backup lights.

It has to be something with the switch, so the next step is how to remove it for further testing and repair or replacement.

Has anyone removed the backup light switch on a manual trans model?

Duke

17 views, no responses - anyone else?

Duke

Here are a couple of pix I took w/ a spare shifter assembly I have. One pic shows the switch from above (looking down onto the shifter assembly while it's still mounted), the other shows the "back end" of the switch. You should see two tabs, one above the swtich's part no. and one below it.

Attached Thumbnails

   

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1990 190e 2.6 - The only one I can really call "My Car".

1987 190e 2.3 - The donor car's up and running, only mods are Euros and a Sony headunit. My Dad's runabout now.

1990 300e 2.6 - The parents' ride.

Thanks very much for posting those photos. Today I removed the plastic "shield" at the top of the linkage that I think is there to keep the rubber boot in proper form.

I removed three of the four bolts leaving the right rear in place. Then I moved the "shield" out of the way at the left front and reinstalled the bolt, then removed the fourth bolt and the shield. My concern was that if I removed all four bolts the bottom of the linkage below the tunnel would fall down.

Once the "shield" was off I could see the two tabs behind the switch with a dental mirror, and you have confirmed that they retain it to the linkage frame as I surmised. There is little room to access them due to the back edge of the console opening being so close, and it looks like I need to dig up a pair of 90 degree tweesers to pinch the tabs together. Do you have a proven way to remove the switch in-place without removing the whole top of the linkage frame?

In the meantime I ran more tests and the switch opens and closes as the plunger is depressed and released either manually or by placing the shift lever in reverse and then back to neutral. The yellow/black input wire has 12v with the ignition switch in the run position, and when I short it to the gray/yellow output wire the backup lights illuminate, but when I install the harness receptacles on the switch pins and exercise the switch plunger either manually or with the shifter - no backup lights!

This is a simple DC circuit with an on/off switch that should not present a major challenge to a 12-year old. What am I missing? I've checked switch continuity using both meter polarities (just in case for some unkown reason the switch has a diode), and it tests okay both ways, and I also swapped the harness wires on the pins with no change in result, so it's just a simple mechanical on/off switch and connector polarity should not be an issue.

The solder connections between the harness wires and the female receptacles appear to be okay both visually and via continuity check. Both the male pins and female receptacles appear clean and corrosion free, but I'm going to do a thorough cleaning tomorrow.

It's just nuts. I can't figure out what I am missing, so any other good minds' analysis will be appreciated.

Duke

Proven method? Sorry. I can tell you that undoing one of the tabs should work; if can get to one of the tabs w/ a flat-blade screwdriver, the swtich should pop right out.

As to your main issue, I can't think of anything else to check w/ the switch or the wiring, so back to the basics (I find simple stuff usually ends up being the problem when I'm in situations like this): 1) I'm not sure which ignition position is the "run" position; is that the position which will energize the fuel pumps? If not, have you tried the ignition in that position? 2) Have you tried both combinations of pins and receptacles?

__________________
1990 190e 2.6 - The only one I can really call "My Car".

1987 190e 2.3 - The donor car's up and running, only mods are Euros and a Sony headunit. My Dad's runabout now.

1990 300e 2.6 - The parents' ride.

Ignition "run" position is the last position before activating the starter motor and the position the switch backs off to when you release the key from cranking. When you turn the key to this position the fuel pump is activated for about one second and all the IP indicator lights illuminate. IIRC the sequence in the clockwise direction is: Off - Unlock - Accessory - Run - Start.

Yes, I've swapped harness wires on the switch pins with no change in test results and continuity checks of the switch using forward and reverse meter polarities (just reversing the test leads) don't indicate that the switch has a diode or any other polarizing feature, so as you would expect with a simple DC on/off switch, polarity is not (or at least should not) be a factor.

Tomorrow I'm going to do a more thorough check of the female pins to harness wire solder joints integrity. That's about all I can think of for now.

Thanks for your additional thoughts.

Duke

Epilog:

The backup light switch operates normally when tested with an ohmmeter, but when you place the circuit load on the switch it DOESN'T WORK!!!

I can't recall ever seeing this, but I talked to a buddy who has a lot of experience with electronics assembly, and he says it happens. In fact, it happened to him about 30 years ago on a mid-seventies 911 he owned.

The switch is on order (about 11 bucks) from my local dealer and should be in on Monday. I managed to remove the switch (press the plastic tabs together) using a paint can opener that has a little hook on the end, and an ancient Look Nevada ski binding tool! It took a few tries, but finally popped out.

I always admonish all to do diagnostics before replacing parts. In this case the diagnostics didn't lead to a logical conclusion, so I spent a lot of time chasing ghosts and scratching my head. I would have been better off just replacing the switch appriori, so in this case doing diagnostics sent my down a blind trail, but that's usually not the case.

I plan on doing a switch autopsy.

Duke

Just when you think you've seen it all...
Once, I went looking for a 0.3 amp current draw on a late 70's Cadillac. I was able to trace it to the circuit that powered interior lights and cigar lighters and such. Then I got stumped. After a -long- while, I managed to trace it to the glove box lamp...WHICH DIDN'T LIGHT UP. In my first go-around on the car, I dismissed the glove box lamp because it didn't light, but sure enough, the switch was passing enough current to kill the battery, but not enough to light the lamp. No difference with the glove box lid open or closed. Pulled the lightbulb and the current draw went away. Sheesh.

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1989 300 SEL that mostly works, but needs TLC