Inoperative dome light - PeachParts Mercedes-Benz Forum

jmcgill · #1 10-30-2009, 08:31 AM

I am stumped as to why my front dome light doesn't work. Before anyone says door switches, my buzzer works when the doors (both) open. ALL the rest of the lights work, rear dome, glove box, trunk lights, etc.

I took the dome light out and tried to see if it was the bulb burned out, but the bulb looks new.

I'm really confused here. Can anyone shed some light on it?

Thanks,

Joe

daw_two · #2 10-30-2009, 08:52 AM

Did you test the bulb by hooking it up to a battery? Looks can be misleading....as most of us know by looking at fuses.

jmcgill · #3 10-30-2009, 08:54 AM

I did better than that, I installed a new one just to be sure....nothing.

ImBroke · #4 10-30-2009, 11:10 AM

I'll be watching. Mine doesn't work either. Just no time to worry about that right now.

toomany MBZ · #5 10-30-2009, 11:39 AM

I find the switch at the light can be a bit picky, Move it back and forth from front to back a few times. It's a three position switch, fully forward, it works with the door. In the middle, it's on all the time. Fully rearward, it's off all the time.

Jeremy5848 · #6 10-30-2009, 11:47 AM

Doesn't the '83 have the version of the dome light with a timer circuit that leaves the light on for a few seconds after you get in the car? If the circuit has gone bad, it won't turn the light on at all.

jmcgill · #7 10-30-2009, 07:36 PM

How would I isolate or fix that circuit?

#8 10-30-2009, 08:01 PM

If you remove the dome light assembly, the circuit board is in the assembly. I would take it out and see if there was any damage.

Yak · #9 10-31-2009, 12:25 PM

Quote:

Originally Posted by toomany MBZ

I find the switch at the light can be a bit picky, Move it back and forth from front to back a few times. It's a three position switch, fully forward, it works with the door. In the middle, it's on all the time. Fully rearward, it's off all the time.

Close, but not quite, in the middle or the "O" position" it's off all the time and the "sunshine with sunbeams" it's on all the time. I think it's possible to install the assembly either way, so front and rear may be irrelevant for troubleshooting and if the door is open that may not help either.

When you say it doesn't work, do you mean "always dark all the time"? Or do you you mean "doesn't work with the door switches but works when I turn it on"?

Remove the assembly, spray some contact cleaner in there, move it back and forth, let it dry, then reinstall. Do the same on the spring clips for the bulb. Probably dirty contacts. Or it might be your bulb, even a new bad bulb. Not the fuse, since other lights are working off of that one.

If that doesn't work and it's REALLY bugging you, then pull out a DMM and check for power at the headliner and check for continuity to ground using the ohmmeter setting (check the lead positions on the DMM) or use a cheapy LED continuity checker.

jmcgill · #10 10-31-2009, 01:18 PM

The light doesn't work in any position, at any time. It's the unit with the timer..I saw the circuitry last night.

I can't spend $79 on a new one right now, so I am in the dark for now.

toomany MBZ · #11 10-31-2009, 03:27 PM

Quote:

Originally Posted by Yak

Close, but not quite, in the middle or the "O" position" it's off all the time and the "sunshine with sunbeams" it's on all the time. I think it's possible to install the assembly either way, so front and rear may be irrelevant for troubleshooting and if the door is open that may not help either.

You're right, good catch.

Yak · #12 10-31-2009, 05:50 PM

Quote:

Originally Posted by jmcgill

The light doesn't work in any position, at any time. It's the unit with the timer..I saw the circuitry last night.

I can't spend $79 on a new one right now, so I am in the dark for now.

Do you have a voltmeter or digital multi-meter (DMM)?

If it doesn't work in any position, then it's probably not the circuitry since it's a direct connection in the sunbeam position. Mine wasn't working and I found out it was both a dirty switch AND a finicky connection with the bulb.

Get a cheap continuity tester, or make one from two test wires with alligator clips and a light bulb. Connect one end to the plain brown wire (I think it's in the three-wire connector) connect the other end to a bulb. Connect the other wire to the other end of the bulb, then touch the other end of that wire to the red wire. Your bulb should light up and you've verified power to the light. If not, then you've got a break in the power wire or in the ground. Neither of these is very likely, but it doesn't hurt to eliminate them as a possibility.

Once you've verified power and ground at the light, then go back and spray the rotary switch liberally with contact cleaner and roll the switch back and forth about 20 times. Shake it out, let the cleaner evaporate. Make sure the bulb is firmly seated in the spring clip and it should work.

Or you've got a busted light.

#13 10-31-2009, 06:18 PM

Also, if I recall correctly the circuit for the dome light goes thought the buzzer relay under the dash. If you are not getting voltage at the dome light, that might be the next thing to check.

Jeremy5848 · #14 10-31-2009, 07:34 PM

Agreed, you need to confirm that there really is 12 volts at the light. The manual-on position of the switch uses the same 12 volt line as the lighted vanity mirrors. If the vanity mirror lights work, the dome light should too. If the '83 doesn't have lighted vanity mirrors there still should be a line at the dome light with constant 12 volts, one with 12 volts when either front door is open, and a ground (brown) wire.

Kelly · #15 11-01-2009, 03:06 PM

I have this problem with my SDL too. I pulled it out, and carefully took the entire thing apart. I assume mine is the time controlled unit because it has a small chip, and several resistors and diodes. Sure enough, half of the chip is fried, and a couple of the resistors are too.

I'm just waiting for one to show up in the JY.

I'm wondering if this may have caused the fuse in the overload protection relay to pop.