I posted this on Benzworld, but only 79mercy took a nibble.

I've been trying to wire my 300D for rear fog lights, but I have been unable to get them working.

I followed the instructions by IQ678 to the letter and for the life of me only the front yellow lights turn on when I pull the knob out into the second position. The little idiot light on the knob as well as the rear lights do not turn on.

I went through every connection and resoldered everything. The ground is running directly to the chassis underneath the cluster.

I have no idea why this isn't working.

Could anyone shed some ideas on my problem?

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Bump

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You could always do the rear fog to extra brake light mod.

Are you sure that you pulled the lamp switch out to the THIRD position?

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Ron Schroeder
'85 300 Turbo Diesel 2 tank WVO
'83 300 Turbo Diesel 2 tank WVO
Some former WVO vehicles since ~1980:
'83 Mercedes 240D
'80 Audi 4000D
'83 ISUZU Pup
'70 SAAB 99 with Kubota diesel
'76 Honda Civic with Kubota diesel
'86 Golf
Several diesel generators
All with 2 tank WVO conversion
LI NY

Very sure. I'm probably going to end up doing that then.

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What third postition? You pull it out to the first position to turn on the front fog's and to the secon position to turn on the rear fog, of which there should be only one.

- Peter.

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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

Yeah it goes only to the "out" one and two position. I read too quickly.

Could the 85's be wired slightly differently? I'm completely stumped.

So here's a detailed description of what happens.

Knob in position 1 pulled out: nothing

Knob in position 2 pulled out: yellow front fogs turn on, rear fog lights and the orange alert light on the knob don't turn on.

I'm completely dumb struck by this!

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That is wierd.
Should be pressed in=all the way off
First indent out, front fogs.
Second, rear and front fogs.

You may have a defective switch.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Wow that might be it. It would have gone un noticed for so many years since it was unused.

I'm certainly bummed now! I'm going to have to get a new switcher now!

Would switching to another point on the device work? There are two open switches on the terminal NSE and one on the outside. What dangerous tom foolery would happen if I swapped the connector from NS to say some other one?

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Good question. I would experiment with spare or junk yard switches first.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Yeah that's a bummer since there aren't any junk yards with benzs in them in my area

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I'm not familiar with the instructions that the OP followed (so please forgive my assumptions) but I am familiar with the wiring of the 1985 300D since I own one.

1. AFAIK, the rear fog light position is not wired to the switch in American cars imported by Mercedes. Perhaps the IQ678 "instructions" were to do this wiring -- my bad!

2. The light in the knob doesn't light because there isn't one. Pull the knob off and you should find no bulb. There may not even be a socket in the American version of the switch. I don't think your switch is bad, at least don't condemn it out of hand.

3. If you do decide to turn the "extra" positions into brake lights, make sure you don't exceed the fuse ratings. Brake light bulbs draw a lot of current. I added an LED-based 3rd brake light in my rear window instead and turned the extra positions into extra tail lamps so I have 4 tail lights and 3 brake lights.

Photos are -- no lights, brake lights, tail lights, all.

Jeremy

Attached Thumbnails

       

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

You are correct! Please don't make fun of me now

When I got into my car after work, I looked at the knob with frustration and pulled it to the right and out. Sure enough when I was in the full right and second position out I pulled it again the knob came off. This time the little idiot light turned on and the rear lights turned on!

So on my 85 300D to turn on the rear head light you have to pull it out into a previously unknown third position. Since there wasn't enough glue on the side of the switch the knob would pull out before I had that chance.

I put some elmers on the side and stuck the knob back on. I'll see in a couple of hours if it did anything!

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