I replaced the headlight switch with a new one. I am nearly 100% certain it is installed correctly. My lights are exhibiting the following behavior:
1. The dash and instrument lights never work (I realize this could be the rheostat).
2. The standing lights never work.
3. Sometimes everything works correctly (with #1 and # 2 as exceptions).
4. Often the right side only works (both running and headlights).
5. Sometimes both headlights work and only the right side tail and running lights work.
6. Foglights work fine.
7. Brake lights work.
8. I know the flasher relay is bad because the blinkers flash funny and the hazard flasher acts up. I have a new one ordered. However, the lights all illuminate when the blinkers are activated, they just flicker fast.
9. Sometimes the behavior of the lights is dependent on the position of the ignition switch. IOW, if the key is off or on can change the function of 3-5.
10. Once when I was fooling with the switch positions I hit the emergency flasher button and all the lights went out.

My questions are: What the heck can cause this? Where can a feller get the good fuses with ceramic body and brass element? Is there a connection where the running light wiring splits into right and left sides (#4 is the most common permutation of the problem)? Can a faulty flasher relay cause any of this?

The car is a blast to drive and I have one turning 16 in several months that is eager to drive the car but I don't like the idea of undependable lights.

Help please!!

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1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".

Remove all your fuses and check that the ends aren't corroded.

-Jason

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Yes remove fuses and clean all the connections, W115's really seem to have issues with dirty fuse connections.

I would also check all the ground wires which can be seen if you remove the headlight door up front, and inside the trunk should be a ground terminal for the rear lights.

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

You need to do more problem definition...

When the problems are exhibited, what can you do to correct or change them? Wiggle fuses? Wiggle switch? Wiggle connectors? Where does the voltage drop out - in the fuse box? At the switch? Try to work on one symptom at a time, you may have multiple problems that need to be sorted out separately.

The best thing you can do is check voltages back from the lights to see where the voltage shows up. You'll find either an intermittent ground or bad fuse connection to be the most likely culprits.

Sometimes symptoms can lead to solutions but electrical issues like this really need to have specifics. "The lights don't work." is not as helpful as "The lights don't work. I have 12V at the fuse but not at the light."

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mjk

'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)

Too fast flashers are a common symptom of a "heavy duty" or double filament bulb in one of the flashers. The heavy filament affects the resistance in the circuit and causes the blinker to act weird - so tip #1 - check all the bulbs for the correct type, not just the correct shape that fits into the socket.

A side effect of a double filament bulb is that it gets hot. Hot enough to melt the sockets and affect the circuit - tip #2 - check the sockets for damage (you may see some 'soot' in the reflector if they've overheated - I had this on a brake light).

I may be confusing something in your terminology, but unless you've got a euro set-up your "running lights" and your "standing lights" are the same, aren't they? If so, then yes they do split so they can be turned on independently (based on the W123 switch, you may have some wacky combination where you need to move the switch to the stand-light position and then turn your turn signal to the side of the car you want the lights to illuminate on - my Audi worked that way).

Do you have a voltmeter? It'll more than pay back in time spent troubleshooting. I'm satisfied with my more/less cheapie Greenlee brand.

Yak, what I call running lights are also referred to as parking lights by some. First click ClockWise on the headlight switch. Standing lights are the right or left side only accessed by turning the switch CCW.

I think I have a large part of my problem licked. The dang fuses in these cars are such a poor design for an otherwise excellent car. I cleaned the fuse "sockets" and installed the few new fuses I have and was able to get all the lights working properly. I am going to buy all new ceramic and brass fuses at first opportunity.

The dash lights still don't work and I tested and there is no power going to them. I checked the plug head that plugs into the back of the cluster and operating the headlight switch did not send power to the terminal.

Also, what are the two small fuse blocks on the driver's inner fender? Two 16A and in a separate box with screw on cover, 2 8A (but only one with wires going to it). I'll take pix later if no one recalls this.

Also does anyone have an extra fuse box cover for this car? Even a picture of the inside of one would help.

Thanks for the replies. Anxious to drive the Great Pumpkin at night!

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1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".

I'm having this same issue.. No dash lights on my 76 w115 and fuse 7 will never hold.


The dash is out and all the side lights are out and the fuse 7 still pops.


What solved your issue and what can I do?