I have '85 300D and my headlights are no longer working. How do you go about dianosing the problem and then repair it?

Check the fuses, see if your fog lights and high beams still work.

Fuses are ok. No low beams or hi beams. Only fog. PO installed euro.

Did both sides fail simultaneously? Check the electrical connections on the back of the lights themselves. If the fuses are ok I dont see what else it could be unless the light switch itself is faulty.

- Peter.

__________________
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

Do your turn signals and wipers still work?

Is it possible the PO may have installed a relay kit for the higher power euro lights?
If they did, you could have a problem with the relay.

__________________
Joe

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1980 300SD - 495k miles - 'The Ambassador'
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Former Family Members
95 C280
73 280SEL
90 300D
87 300SDL (X2)
86 560SEL
84 300D
80 300SD

Wipers, blinkers and other equipmant all work. I've checked the plug into the headlight itself.
It seems that I started having problems when the rf(passenger side) six prong plug started to come loose and when blinker lense and bulb on the same side was broken by a rock from the hwy. Although, this could be just a coicidence.
Does'nt it seem more likely to be problem with wiring(ground) or perhaps a relay, rather than the headlight switch itself?

Many thanks for all the ideas.

Please do the following:

1) Try and "flash" the brights. With the vehicle running, pull the stalk toward you and see if the brights will flash. I'm not interested in the normal running position for the brights.......with the stalk all the way back.

2) If yes, then report back.

3) If no, then replace fuse #6 and try it again. Don't look at the fuse and don't report back that the fuse was OK. Just replace it.

4) Report back with results.

Brian, What color / amperage is that fuse supposed to be ?
Just in case someone put one too low in it.....
To make this test faster ( than driving to the autoparts store ) , is their one of the correct size in the fuse box which could just be moved over to there ( or swapped , which , if the newly served circuit quit would show the fuse to be bad no matter how nice it looked ). ?

That's a 16 amp fuse that's used for flashing the headlights and also to run the wiper/washer. Any red fuse should be fine for testing.

So, if the wiper/washer works, the headlights should flash.

It's just one step in the diagnosis.

Ok I did the test that Brian suggested. When I pulled the stalk back, toward driver, only the left front flashed. What to do?

Go in the fuse box and replace fuse #7. It's a white 8 amp fuse. Make sure you replace it with a new one and clean the contacts.

Repeat the test and see if both high beams flash.

Ok, I thought I had a white 8amp fuse but I don't. So I'm off to meglo mart. I didn't change fuse # 6, even though the left side of the high beam flashed and not both. Right?

While I'd prefer that you replace any fuse that we discuss, the fact that one headlight functions and the other does not will effectively rule out fuse #6 in the flash mode.

The problem with diagnosing electrical issues on these vehicles is that they can be intermittent when dealing with old fuses. Sometimes the problem will manifest itself.......sometimes it won't. Troubleshooting such an issue is basically impossible. Hence the reason to replace any fuse involved in the discussion.

You definitely need to carry spare fuses on any vehicle of this type, so a trip to McParts is certainly warranted.

The better fuses, with copper conductors, can usually be found at NAPA or online.

Ok it seems as though what I thought originally that my left headlight flashed, now niether one flash when I pull back the stalk.