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Rear marker lights and brake lights not working. But turns, 4 ways and reverse are working.


Rotorhead
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Hello All,

Ah another issue. Found out the hard way (pulled over) that my rear marker lights and brake lights are not working. The turns, 4 ways and reverse lights are all working. I cleaned all the connections and checked all the fuses that had anything to do with lights. They all looked good except a few had a blackish/brown residue on the prongs. I cleaned that off.

Any ideas on what I should check next?

Sorry for so many questions.

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3 minutes ago, Rotorhead said:

Hello All,

Ah another issue. Found out the hard way (pulled over) that my rear marker lights and brake lights are not working. The turns, 4 ways and reverse lights are all working. I cleaned all the connections and checked all the fuses that had anything to do with lights. They all looked good except a few had a blackish/brown residue on the prongs. I cleaned that off.

Any ideas on what I should check next?

Sorry for so many questions.

What kind of vehicle?

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I am not a Gen II owner and, therefore, have not ventured into those schematics much.  I opened them this A.M. and tried to trace through them to find the path for brake lights.  They pass through the Lighting Control Module.  If you are not getting any codes for light faults, I would want to start there or before it.  The LCM should throw a code if it knows there is a request for that lamp to work.  I would start by finding the brake pressure switch (direct input to the LCM) and see if it is working. 

Check the trailer connector brake pin and see if it is getting 12VDC (bottom right pin if running a RV 7-way).   Are you running a jackalopee?   If so, is the LED for brake lights coming on?

 

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Hi,

I just got the truck last week so no modifications yet.

The problem is on the truck. I was going to test the 5 places on the fuse panel for each of the 5 LCM fuses. Unfortunately they are not marked as to what each one goes to.

I am assuming there is a brake switch at the top of the brake pedal under the dash like a passenger car?

Other than than I guess I will have to have a shop take a look.

Thanks again for all the replies. Gaining more knowledge is always great!

Chuck

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19 minutes ago, Rotorhead said:

Hi,

I just got the truck last week so no modifications yet.

The problem is on the truck. I was going to test the 5 places on the fuse panel for each of the 5 LCM fuses. Unfortunately they are not marked as to what each one goes to.

I am assuming there is a brake switch at the top of the brake pedal under the dash like a passenger car?

Other than than I guess I will have to have a shop take a look.

Thanks again for all the replies. Gaining more knowledge is always great!

Chuck

There is not typically a switch on the brake pedal like you would find in a car. On my Gen 1, it's a switch on an air line inside the dash. Jay

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14 hours ago, Rotorhead said:

Hello All,

Ah another issue. Found out the hard way (pulled over) that my rear marker lights and brake lights are not working. The turns, 4 ways and reverse lights are all working. I cleaned all the connections and checked all the fuses that had anything to do with lights. They all looked good except a few had a blackish/brown residue on the prongs. I cleaned that off.

Any ideas on what I should check next?

Sorry for so many questions.

Hi Rotorhead,

Don't be afraid to question question. This is how you are going to learn about your truck. This is a good group of guys always willing to help. Also let YouTube be your friend. You can be surprised what you can find. Don't ask me how I know. 🤣    Al

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We have a gen 1 so it may be different, but there's a little door in the top of the dash right in front of the steering wheel.  Open that, and if your lucky, you'll see a brake switch, maybe two.  Also, the underside of the fuse cover has a list of all the fuses.  But, those darn numbers and letters at the fuses are so tiny and it's dark in there.......

Good luck.  And remember, with 12v, it's usually a grounding issue.

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12 hours ago, Rotorhead said:

Hi,

I just got the truck last week so no modifications yet.

The problem is on the truck. I was going to test the 5 places on the fuse panel for each of the 5 LCM fuses. Unfortunately they are not marked as to what each one goes to.

I am assuming there is a brake switch at the top of the brake pedal under the dash like a passenger car?

Other than than I guess I will have to have a shop take a look.

Thanks again for all the replies. Gaining more knowledge is always great!

Chuck

There is a switch up high on the brake pedal.  It has a feeler to sense the motion of the brake pedal.

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Awesome thanks Sculptor. I will try to locate it this week.

I pulled the rear lights and on each one the higher filaments were not broken but had the same deformities. Like they burnt or wanted to burn. I have new ones on the way. We'll see what happens with that. I also have no codes for the Light Control Modules so I just have to keep looking.

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Again thanks for all the replies. I did call the local Volvo Dealer and he told me the switch should be marked SLS for Stop Light Switch I believe. I will certainly dig around and learn about it.

Once I get my TLC obvious list done then I can start the conversion process. More questions on that later. Hopefully we will get to a rally. That will be fun.

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I decided to pull the lights and get a look at the filaments. (should have started with that). The picture isn't the greatest due to small file size but you can see the higher filament is definitely not the same as the lower. It appears to be connected but something happened to it. It is the same on both fixtures. So I ordered two more Type 60 incandescent fixtures. Hopefully that is my problem. Now the question is will the LCM need to be reset? Will it reset itself during the self test when you turn the key? There are no LCM faults. 

I did learn that the turn and 4 way share the lower filament, which means the marker and brake share the upper one.

rear light.jpg

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1 hour ago, rickeieio said:

4 way, turn and brake are one filament, run/marker is the other.  Either you have a bad ground, or someone's fiddled with your wiring.  I'm betting on the former.  Try running a wire from battery negative to the bulb base.

What he said ^^^^
 

At least on my truck the LCM is very obnoxious and informative if something is not working right. And yes it should reset with a power off. 

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Awesome thanks. Got thunderstorms today so have to wait til tomorrow to check the ground to the bulb base.

I did check all the connections I could find related to lights. One had minor corrosion and the license plate connection had a decent amount of corrosion. Cleaned and dielectric greased.

I found two small grounds on the firewall above the big wires from the battery. Those ones were good. 
at least when I am done I will be very familiar with all that wiring. Haha.

thanks again I appreciate all the help.

Chuck

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I was able to get out and test the wires at the light fixture connection. With just the light switch turned to the marker position there is basically 5.6 volts at the connection on the black wire and nothing on the red.

wish I had the schematic. Hopefully no storms tomorrow so I can get in and check the brake light switch. And look for any ground points that need attention.

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Black should be the marker, red the turn/stop. With the power coming from the LCM, you really need to have the bulb connected to get good readings. The power is switched by semi conductors, so you can get some weird readings with no load on the circuit.

Have you checked for power on the trailer cord? The trailer lights are switched by a relay box under the hood by the steering shaft.

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15 minutes ago, Moresmoke said:

Have you checked for power on the trailer cord? The trailer lights are switched by a relay box under the hood by the steering shaft.

In about the ninth post, he says the issue is in the truck.  I don't believe a trailer or associated wiring is in the picture.

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13 minutes ago, rickeieio said:

In about the ninth post, he says the issue is in the truck.  I don't believe a trailer or associated wiring is in the picture.

Yes, but you can often tell if the circuit is working by checking the trailer plug. That would isolate the problem to the light and its fixture. Jay

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