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ehenry8
join:2007-11-07
Gilson, IL

ehenry8

Member

Stumped by tail lights.

2004 Dodge Ram

Tail lights are not working. I have checked.
--All bulbs
--Wiring under truck looks good
--Fuse for "Tail and Park Lamps"
--All turn signals work
--All backup lights work
--All brake lights work.
--No front or back park lights
--No License plate lights.
--No Running Lights for trailer hitch

Any ideas?

psafux
Premium Member
join:2005-11-10

psafux

Premium Member

said by ehenry8:

2004 Dodge Ram

Tail lights are not working. I have checked.
--All brake lights work.
--No front or back park lights
--No License plate lights.
--No Running Lights for trailer hitch

Obtain a wiring schematic and find out what all those have in common & you will likely have your answer. My initial assumption would be a ground.
ehenry8
join:2007-11-07
Gilson, IL

ehenry8

Member

said by psafux:

said by ehenry8:

2004 Dodge Ram

Tail lights are not working. I have checked.
--All brake lights work.
--No front or back park lights
--No License plate lights.
--No Running Lights for trailer hitch

Obtain a wiring schematic and find out what all those have in common & you will likely have your answer. My initial assumption would be a ground.

I looked over the diagrams and looks like they all use the park lamp relay. Is there a good way to test a relay using a volt meter or something?

psafux
Premium Member
join:2005-11-10

psafux

Premium Member

Sure, you can test for voltage & continuity.
ehenry8
join:2007-11-07
Gilson, IL

ehenry8

Member

And can anyone tell me where the G104 ground is located?

Jim2112
@insightbb.com

Jim2112 to ehenry8

Anon

to ehenry8
To test the relay just tap on it with the circuit energized (light on). They get stuck and a little banging will get them to flip. If the lights come on after banging on the relay, then it's time for a new relay.

pmohr
Premium Member
join:2002-09-22
Maryville, TN

pmohr to ehenry8

Premium Member

to ehenry8
Saw this exact problem a little while back on a newer Grand Cherokee, needed a control module on the underhood fuse box. IIRC there was signal in to the module for parking lights, just no signal out.

Should be a similar setup in your truck.
ehenry8
join:2007-11-07
Gilson, IL

ehenry8

Member

said by pmohr:

Saw this exact problem a little while back on a newer Grand Cherokee, needed a control module on the underhood fuse box. IIRC there was signal in to the module for parking lights, just no signal out.

Should be a similar setup in your truck.

Is this module mounted to the side on the fuse box. What is the proper way to test this?

pmohr
Premium Member
join:2002-09-22
Maryville, TN

pmohr

Premium Member

said by ehenry8:

Is this module mounted to the side on the fuse box. What is the proper way to test this?

Yes, it was mounted on the fuse box.

Turn the headlight switch on, check the appropriate input wire at the module, then check the output for the parking lights from the module.

I don't have the FSM or an electrical diagram for your truck, so I couldn't tell exactly which wires you need to go after. It should be fairly obvious with a decent wiring diagram.
ehenry8
join:2007-11-07
Gilson, IL

ehenry8

Member

said by pmohr:

said by ehenry8:

Is this module mounted to the side on the fuse box. What is the proper way to test this?

Yes, it was mounted on the fuse box.

Turn the headlight switch on, check the appropriate input wire at the module, then check the output for the parking lights from the module.

I don't have the FSM or an electrical diagram for your truck, so I couldn't tell exactly which wires you need to go after. It should be fairly obvious with a decent wiring diagram.

So i did some looking and it seems the FCM is mounted under the fuse box and the only way to get to it is to disconnect the fuse box and battery cables. If this is true how do you test it?

pmohr
Premium Member
join:2002-09-22
Maryville, TN

pmohr

Premium Member

said by ehenry8:

So i did some looking and it seems the FCM is mounted under the fuse box and the only way to get to it is to disconnect the fuse box and battery cables. If this is true how do you test it?

Wouldn't be able to say without actually seeing it, but there's likely a section of harness in an accessible area you could test at.

MooJohn
join:2005-12-18
Milledgeville, GA

1 edit

MooJohn to ehenry8

Member

to ehenry8
Assuming you have the factory tow package (not spliced into the rear tail wiring), it could be fuse # 5 (7.5 amp). This diagram shows it would stop both the parking lights and the trailer's blinker outputs from working.




It could also be the parking relay itself. Try swapping it with another relay to see if that makes the lights work. They're labeled on the underside of the fuse box cover.

This diagram is from my 2003 Ram but I don't think they changed anything in this area.

Oops - now I see that it says that's a PTC, not a fuse. The abbreviation escapes me at the moment so I don't know what that refers to. It feeds the Front Control Module so if it isn't the relay itself you could need a new FCM.

Do you have fog lights? The FCM controls that too, and the horn.
ehenry8
join:2007-11-07
Gilson, IL

ehenry8

Member

Yes i have fog lights and headlights....horn works as well. Seems to be just tail light and front park lights as well as license plate lights.

--Brake lights work
--Turn signals work front and back
--backup lights work
ehenry8

ehenry8

Member

I can post the wiring diagram for my truck if someone here can help me read it properly.

pmohr
Premium Member
join:2002-09-22
Maryville, TN

pmohr

Premium Member

said by ehenry8:

I can post the wiring diagram for my truck if someone here can help me read it properly.

Go ahead and post it, and we'll take a look.

mattmag

join:2000-04-09
NW Illinois

mattmag to pmohr

to pmohr
said by pmohr:

Wouldn't be able to say without actually seeing it, but there's likely a section of harness in an accessible area you could test at.

How do you suggest he test said harness, once that "section" is visible?

pmohr
Premium Member
join:2002-09-22
Maryville, TN

pmohr

Premium Member

said by mattmag:

said by pmohr:

Wouldn't be able to say without actually seeing it, but there's likely a section of harness in an accessible area you could test at.

How do you suggest he test said harness, once that "section" is visible?

Exactly as I mentioned above. Not sure what you're getting at.

mattmag

join:2000-04-09
NW Illinois

1 recommendation

mattmag



I am getting at the method of testing a wiring harness mid-length such as in this situation. I am hopeful you aren't advising him to poke a hole in the side of the wires for testing purposes? Harnesses should only be tested at termination points to prevent future issues with moisture and corrosion from having the insulating jacket damaged during improper testing.

I'm guessing you know that, but the OP may not be aware.
ehenry8
join:2007-11-07
Gilson, IL

ehenry8

Member

Click for full size
8W-51-2.pdf
130,196 bytes
License plate light--not working
Click for full size
8W-51-6.pdf
117,808 bytes
Tail Lamps not working, turn signals work.
Click for full size
8W-51-7.pdf
157,545 bytes
Brake Lights--Working Fine
Here is the diagrams. If you could take a look and see what you think. Thanks for the help guys!

ironweasel
Weezy
Premium Member
join:2000-09-13
Belen, NM

ironweasel to ehenry8

Premium Member

to ehenry8
Did anyone check to see if there was a TSB for that model year regarding the tail lights?

I used to work at a local Dodge dealer just doing basic stuff like oil changes, batteries, light repairs, crap like that and I seem to remember that there were issues up the wazoo with the tail lights on the Rams not working because the circuit board on the lights themselves would burn up. However, I don't recall if there was a TSB for that year, but 9 time out of 10 when someone came in with no tail lights, it was because the circuit board had crapped out.

Just throwing that out there as a suggestion.
xj31
join:2005-09-25
Lake Villa, IL

1 recommendation

xj31 to ehenry8

Member

to ehenry8
I doubt it's a ground problem.All the lights have different grounds,so for the front and rear to not work you would have to loose a lot of grounds at once.Also some of the grounds are shared by other things so I think you would have more problems.
Jim2112 has a good idea about the relay,its a definite possiblity.You checked the fuses,fuse 15,the 50 amp is the main one.I would pull the park lamp relay and check for 12 volts at terminals 85 and 30.If thats good,you can jump 30-87 and see if the lights work.That will check the wiring and grounds all at once.
If that works,I would swap the relay with one that you know works like the starter or fuel pump relay.Then you know if the relay is good or not.
If that doesn't do it,now it could get tricky.The switch is actually wired to the instrument cluster.The cluster sends a bus message to the FCM and thats what decides what to do with the park lamp relay.So it sounds like your problem is on the hot side of the circuit.Switch,relay or FCM.
I dont know if this helps or not,but that's how I would start testing it anyways.

Xstar_Lumini
join:2008-12-14
CANADA

Xstar_Lumini to ehenry8

Member

to ehenry8
Ironweasel's explanation is a very plausible one for this problem.

ironweasel
Weezy
Premium Member
join:2000-09-13
Belen, NM

ironweasel to ehenry8

Premium Member

to ehenry8
Go to Rockauto or do a Google search for "Dorman 70030". Those are the circuit boards I'm talking about. Rockauto has them for like $9 and some change + shipping for each side. To get to them, you just remove the tail light housing and the circuit board is screwed to the rear of the housing.

Again, I don't remember if there was an actual TSB issued for that or not, but I know there was something on DealerConnect at the time regarding the tail lights, so it may have just been a service campaign instead of an actual TSB.

mattmag

join:2000-04-09
NW Illinois

mattmag to Xstar_Lumini

to Xstar_Lumini
said by Xstar_Lumini:

Ironweasel's explanation is a very plausible one for this problem.

How is that plausible?
said by ehenry8:

--All turn signals work
--All backup lights work
--All brake lights work.
--No front or back park lights
--No License plate lights.
--No Running Lights for trailer hitch

The taillight printed circuit boards DO NOT affect the operation of the front parking lamps, nor are they related to the license plate lights, or the taillight circuit for the trailer connector.

The diagnostic steps from xj31 See Profile are a much better plan than a shot-in-the-dark "put taillight boards in it" suggestion. No offense, ironweasel, but proper electrical diagnostics should be performed on any such electrical problem before parts are thrown at it.

MooJohn
join:2005-12-18
Milledgeville, GA

MooJohn to ehenry8

Member

to ehenry8
This topic came up today on DodgeForum.com

»dodgeforum.com/forum/3rd ··· 0-a.html

It may guide you right to the solution. You've already got the manual so look for connectors C2 and C3 and see if they're corroded or have damaged traces.
ehenry8
join:2007-11-07
Gilson, IL

ehenry8 to xj31

Member

to xj31
said by xj31:

I doubt it's a ground problem.All the lights have different grounds,so for the front and rear to not work you would have to loose a lot of grounds at once.Also some of the grounds are shared by other things so I think you would have more problems.
Jim2112 has a good idea about the relay,its a definite possiblity.You checked the fuses,fuse 15,the 50 amp is the main one.I would pull the park lamp relay and check for 12 volts at terminals 85 and 30.If thats good,you can jump 30-87 and see if the lights work.That will check the wiring and grounds all at once.
If that works,I would swap the relay with one that you know works like the starter or fuel pump relay.Then you know if the relay is good or not.
If that doesn't do it,now it could get tricky.The switch is actually wired to the instrument cluster.The cluster sends a bus message to the FCM and thats what decides what to do with the park lamp relay.So it sounds like your problem is on the hot side of the circuit.Switch,relay or FCM.
I dont know if this helps or not,but that's how I would start testing it anyways.

Ok i have 12volts to both 30 and 85. I jumped 30 and 87 and lights come on. I swapped out the relay with the starter relay. Nothing happened. So the question now is what makes the relay engaged? Is it the switch in the dash or the FCM. I will check out the link posted above but any more insight is appreciated. Thanks.
xj31
join:2005-09-25
Lake Villa, IL

2 recommendations

xj31

Member

Ok now you're getting somewhere. Unfortunately, this is where it gets complicated. It could be the switch,or the front control module. The problem is that the switch is wired to the instrument cluster which sends a bus message to the FCM which then energizes the park lamp relay. So its not just a simple check of wiring with a multimeter. On your truck,the FCM is built into the fuse box under the hood.They call it the IPM or integrated power module. They might call it the PDC or power distribution center. Whatever you want to call it,it's kind of a common problem on those trucks,and I think its about $300.00. I hate to guess,but if I had to, that's what I would be leaning towards. You really need a DRB 3 scan tool to diagnose it now.
ehenry8
join:2007-11-07
Gilson, IL

ehenry8

Member

said by xj31:

Ok now you're getting somewhere. Unfortunately, this is where it gets complicated. It could be the switch,or the front control module. The problem is that the switch is wired to the instrument cluster which sends a bus message to the FCM which then energizes the park lamp relay. So its not just a simple check of wiring with a multimeter. On your truck,the FCM is built into the fuse box under the hood.They call it the IPM or integrated power module. They might call it the PDC or power distribution center. Whatever you want to call it,it's kind of a common problem on those trucks,and I think its about $300.00. I hate to guess,but if I had to, that's what I would be leaning towards. You really need a DRB 3 scan tool to diagnose it now.

So the fuse box and FCM is the same thing....or are they sold seperately and I have to merge them upon installation....can i test switch before dropping 300 bucks on a FCM?
xj31
join:2005-09-25
Lake Villa, IL

xj31

Member

I can't find the actual ohm specs for the switch.I guess you can just test and make sure you have something when you turn it on.Seriously,the scanner is invaluable for this.The fuse box/FCM/IPM is one piece.I would hate to tell you to drop the cash on it,even though past experience says that's it.I just hate throwing parts at something.I'll keep looking for the ohm specs for that switch.
xj31

xj31

Member

Click for full size
This is how the switch is wired.