No License Plate Lights

[ScottyP]

My Trunk Lights and License Plate Lights stopped working on my 95 C280. The bulbs and fuse is good. But, Im not sure if another fuse is causing the problem. Ohm tested both and found no power is reaching them.. What should I test next?

Glove box and all interior lights are working. Help!!

[therock2689]

pop off the truck lid carpet and check the wireing from the light as far as you can. Somewhere you probly lost a ground or a terminal sliped off or something you you might have cut it somewhere working on something, maybe. just check teh ground for that and the power terminal. If al else fails, just run a new circuit using the running tailight power and make a ground or something like that.
Good luck hope you can figure it out.


Roca

[ScottyP]

Thanks Roca,
I have the the truck lid carpet off. I traced the wires from the lid to the back deck on the passenger side.

Im thinking of using your suggestion and just running a new circuit. But, which line in the tailight is the power line to use?
Scotty

[SLAMMED_C]

check the wires in the trunk lid hinge.. they are probably broken.. I think the right side hinge has the wires in it. have a look and you will probably find they are broken.
just splice in some new wire where the break is.. add about an extra 3-4 inches of wire in place of the break.

[therock2689]

If you are going to run a new one, just turn on the cornor lights, teh first click of the headlight switch, and then grab you test light. find out which is lighting teh bottom row of lights(thats how it is on my 2000 c230k). just dplice out of and then run a new ground. not to hard.
Good luck, if you need more help just hit me up.
Good juck


Roca

[ScottyP]

Thanks to both of you for recommendations. I will try that now.. You are correct, the wires are enclosed in a black cover but no breaks found yet. Im goin to find this tonight!! Or rewire the whole thing!!

[SLAMMED_C]

the break will be near the base of the hinge.. where it curves back into the trunk side panel..
if there is a break.
you check power and ground at the license plate lights.. and you have neither?
I cant remember what else is on the same fuse as the license plate lights.. but if there are other things and they work fine.. it leads me to believe a break in the wire in the hinge over anything else.
have a look.. hopefully you find it.

[ScottyP]

Originally posted by SLAMMED_C
the break will be near the base of the hinge.. where it curves back into the trunk side panel..
if there is a break.
you check power and ground at the license plate lights.. and you have neither?
I cant remember what else is on the same fuse as the license plate lights.. but if there are other things and they work fine.. it leads me to believe a break in the wire in the hinge over anything else.
have a look.. hopefully you find it.

Okay, found a crack at the joint where it goes to the side panel. But its not broken through. Just the wire cover is cracked. Im cutting that out and replacing the section. Hopefully this is whats causing the problems with the license plate lights. But wheres the wires between the trunk switch and the trunk light?

[SLAMMED_C]

Originally posted by ScottyP
Okay, found a crack at the joint where it goes to the side panel. But its not broken through. Just the wire cover is cracked. Im cutting that out and replacing the section. Hopefully this is whats causing the problems with the license plate lights. But wheres the wires between the trunk switch and the trunk light?

the wires for the trunk switch and trunk light should be in the same place... they all may share a same feed.. probably same ground or soemthing. but the wires should be in the same hinge.. or maybe they are in the other side.. I cant remember.. sorry.

[strictlyspeakin]

The only common point between the trunk lid courtesy light
and the license plate lights (left and right) is the ground. They share the same ground point (right tail light ground).

Test for ground on these lines and it's likely missing. I'm puzzled by the fact that you didn't see 12V+ during your test. Did you go directly to a known good ground during your test? Where were you testing for it?

[ScottyP]

Originally posted by strictlyspeakin
The only common point between the trunk lid courtesy light
and the license plate lights (left and right) is the ground. They share the same ground point (right tail light ground).

Test for ground on these lines and it's likely missing. I'm puzzled by the fact that you didn't see 12V+ during your test. Did you go directly to a known good ground during your test? Where were you testing for it?

Replaced the cracked section of the wire. STILL no lights!!!

I tested for 12V+ at the lights. I did use a known good ground. Used the Amp ground point.

Where is the ground located on the right tail light ground? Which wire?
Is anything else connected to this ground? (like the right tail light?)

[therock2689]

you can make a ground. just take out the paint and drill a hole, crip a ring terminal on a wire. Now you have an instant groung pt.

[strictlyspeakin]

I'll check tomorrow :tired:

[strictlyspeakin]

Ok stop me if you've got something different.

The 12V+ lead for the license plate lights is: Red, Grey, Blue.
The Ground wire is: Brown (real surprise there)

So take your ohm meter and measure the resistance between the Brown wire and your known good ground point by your amp. You should not have any. The brown wire runs from the left license plate light to the right license plate light and from there to the ground point. So I'd test at the right light and remove the light bulb to make sure.
Once we establish if ground is there we can go after the 12V+.

Next go to the trunk lid switch. Test the resistance for the Brown wire on that to the same known good. The Brown,White wire comes from the trunk light.

To answer your question, pin 6 on the Right tail light harness should be grounding to the same point, but I do not think that the trunk light/license plate lights run to pin 6. Ground point is in trunk against right wheel well I'm pretty sure anyway.

Keep me posted.

[ScottyP]

So take your ohm meter and measure the resistance between the Brown wire and your known good ground point by your amp. You should not have any.

None. Zero resistance

The brown wire runs from the left license plate light to the right license plate light and from there to the ground point. So I'd test at the right light and remove the light bulb to make sure.

switch on;
removed the left bulb - no light
removed the right bulb - no light

Next go to the trunk lid switch. Test the resistance for the Brown wire on that to the same known good. The Brown,White wire comes from the trunk light.

None. Zero resistance

i believe i have ground but no power.

[strictlyspeakin]

Wow, I was sure it was going to be a ground.
Tomorrow, well later today anyway, I'll check where the power comes from.
Till then, test resistance across the trunk lid switch. I presume it works though.
Were those 12V+ wires I mentioned the same color?

[ScottyP]

Originally posted by strictlyspeakin

Wow, I was sure it was going to be a ground.
Tomorrow, well later today anyway, I'll check where the power comes from.
Till then, test resistance across the trunk lid switch. I presume it works though.
Were those 12V+ wires I mentioned the same color?

Well, tonight I finally fixed the problem with the license plate lights and the trunk light.

Here's how I found it:

1. Performed all of the ohm test and got no readings as you stated - 0 ohms. BTW, the ground wires were Brown and the power wire is Red.

2. Fustrated after pulling the cover off and testing the wires several times over a week now, I decided to do some additional tests for power. Using the trunk lamp for portability , connected one side of the lamp to a known good ground (trunk latch), and the other side to the red power wire in a few places looking for power. The first place was at the License lamp, next test at the hinge splice made last week, then the wire went into a cloth tube about 3 foot long. So I decided to splice at the far end of the tube near the rear seat. Tape was wrapped around that end to hold the cloth tube in place. I removed the tape and located the Red wire.

3. While pulling the wire to splice, I notice the wire was moving freely. And what you know, it was cleanly cut about 5" down the cloth tube. Stripped the end and connected to the portable lamp and Behold - - We have LIGHT ! !

4. Now to repair the red wire. While repairing stripping the other end of the red wire inside of the cloth tube, 3 other wires fell out of the tube. Now, Im pulling all of the wires looking for other breaks. The Red, Black, Brown for the license lamps and the other Brown for the Trunk Light switch were all evenly spliced (INSIDE THE CLOTH TUBE & THE TUBE HAD NO EXTERIOR DAMAGE or MARKS). Well, now Im puzzled how did this happened and why wasnt the other 3 wires in the tube intact? :werd:

5. Not taking a chance of future problems and suspecting this was just German wiring deterioration, I replaced all the wires in the tube from the back seat to the devices with good ole American wiring from AutoZone (probably made in China or Mexico)..

6. Now, my trunk light is working properly, and I have License Plate lights.

PROBLEM FIXED.. :banana:

I had no 12v power, no trunk light ground, no license light ground and no connection to whatever the black wire controls...
But, Im a happy camper now...

Thanks for everyones help.. especially strictlyspeakin !

NOTE: The Ground for the Trunk light and the Ground for the License Plate lamps are separate wire and are not interchangeable!!
If you switch them, neither unit will work. Ask me how I know...

Now, Im in search of whats killing my Backup light !!
Anyone knows which harness wires in the tail lights control the Backup (Reverse) lights??
(I really need to find a wiring diagram for this car with these strange color codes: Brown for Ground; who would have thought!)

[Proven Guilty]

i had an old chevy beretta, and the backup lights would intermittently fail due to a faulty nuetral switch (has to do with the transmission).

for the chevy is was like an $80 part... but i may be throwing darts with your wiring problems previous to this!

[ScottyP]

Thanks..

Ive also had this problem with a G20 Chevy Conversion Van. The Mercedes appear very different. Tested the wires at the switch and have power there and the ground wire tested good too.
But dont have power at the backup lights. There is a break somewhere between the switch and the backup lights themself.

I will do additional testing tommorrow and Saturday. Im determined to fix all of my wiring problems.

[strictlyspeakin]

Scotty. - more food for thought.......

Left backup light is pin 3 -Yellow and Grey for 12V+
Right backup light is pin4 - Yellow and Grey for 12V+

Both of these wires go to the same point. Behind the right front kick panel. From there a single wire heads out into the engine compartment behind the left front headlight. Finally continuing on to the starter lockout switch on the left side of your transmission. The 12V+ comes from fuse 31 in your fuse box.

Start by checking for 12V on pin 5 at the connection inside the engine compartment. pretty sure you'll get it. Then move to pin 6. The car has got to be on and in reverse to do this though. This will test your starter lockout/backup switch. (likely failure point) But considering your funky wiring failure maybe not.

PM me your email and I'll send you a picture of where that connection in the engine compartment is.



(ground wires are still Brown )
0 ohms from a brown wire to a known good ground is a good thing btw. It means that there is no resistance and the circuit is continuous; ie the ground is good.

[ScottyP]

[PM me your email and I'll send you a picture of where that connection in the engine compartment is.

PM Sent

(ground wires are still Brown )
0 ohms from a brown wire to a known good ground is a good thing btw. It means that there is no resistance and the circuit is continuous; ie the ground is good. [/B]

So, if the brown-ground wire is broken somewhere, why am I not getting resistance? I didnt get resistance with the cut ground wires in my trunk & tag lights. Should the car be on to test this too? I thought ground is ground (even if brown); no power necessary. Or is this just on the Mercedes?

Hopefully, you are right with the bad switch theory. I would rather change a switch than tracing these wires thru all the nooks.

[strictlyspeakin]

I'm no electrical engineer by any stretch, but in my simple mind, resistance is a measure of the amount of effort it takes the electricity to go between two points. Your voltmeter has a battery in it and when you test resistance it sends a small amount of voltage down the line to

So if you had a broken wire the resistance would be infinite, which is usually represented by 1 on most digital voltmeter/ohmeters.

If you had a solid wire and two clean connections on both sides, you would get a resistance measure of 0. Electricity could flow without any problems.

If you had a solid wire but two dirty connections you would see values of >0 but <1.

There are of course other reasons for resistance on the line, but these wese just a simple examples.

You said your brown wire had resistance of 0 between the tag light and your amp grounding point. So that would indicate a good solid ground to me. Your point of failure seemed to be the 12V wire that you found broken.

You are correct. power isn't necessary for for resistance tests. "even if brown" hehehe. Talk to you tomorrow...er...later today.

[ScottyP]

Originally posted by strictlyspeakin
Scotty. - more food for thought.......

Left backup light is pin 3 -Yellow and Grey for 12V+
Right backup light is pin4 - Yellow and Grey for 12V+

Both of these wires go to the same point. Behind the right front kick panel. From there a single wire heads out into the engine compartment behind the left front headlight. Finally continuing on to the starter lockout switch on the left side of your transmission. The 12V+ comes from fuse 31.

Start by checking for 12V on pin 5 at the connection inside the engine compartment. pretty sure you'll get it. Then move to pin 6. The car has got to be on and in reverse to do this though. This will test your starter lockout/backup switch. (likely failure point)

Hi all..
Im finally back off the road on business. Had time to investigate this weekend.

First, Fuse 31 does not supply power. It is listed as vacant and currently dont have a fuse in it. This is a late model 95 C280 w/odb2.

Second, tested the pin 5 at the connection. NO Power. Then tested pin 6 with car on and in reverse. NO Power. I did not get the 12v reading on either pin.

So, now Im trying to figure this out. Which fuse provides power to the backup lights?
Whats the order: fuse -> lockout switch -> 25pin connection -> right foot panel wires -> backup lights??

Ideas anyone?

[strictlyspeakin]

Hey just noticed this looks like I left Scotty hangin...

After some offline help his wiring is more like a 94 than a 95. His fuse power was #29. That and a good ground got him power on pin 5. Pin 6 still dead.

So he's off to looking at the starter lockout switch.

Wonder how he's made out???

[ScottyP]

Originally posted by strictlyspeakin
Hey just noticed this looks like I left Scotty hangin...

After some offline help his wiring is more like a 94 than a 95. His fuse power was #29. That and a good ground got him power on pin 5. Pin 6 still dead.

So he's off to looking at the starter lockout switch.

Wonder how he's made out???

You didnt leave me hanging... I was putting off crawling under the car until today. Lots of stuff to do and this is just one of my repair chores.

Fuse 29 was fine.. Removed the lockout switch and cleaned it up. Really wasnt in bad shape. Reinstalled and no backup lights.
How can I test it? It has 4 terminal connectors (two at each end of the connector). Can I test for resistance to verify if its the culprit?

I really suspect a wiring problem but I would like to rule out the Neutral Safety Switch first. Order a new one but it does not match the one on the car (New one is all metal, on the car is metal & plastic).