Electrical/lighting issue

DODGEMAN72

MEMBER
2002 DODGE RAM
5.9L
V8
4WD
AUTOMATIC
160 MILES

Hi,
I am having an issue that is driving me crazy.
The only physical problems are right brake light will not light, and the right turn signal is a little fast (not hyper speed, but faster than the left).

Before I explain the weirdness of it, let me tell you what I have already done:

I have replace all rear stop/turn/tail light bulbs. No joy!
Replaced the right rear socket assembly. No joy!
Replaced the body module, or FCM. No joy!
Opened, inspected, and cleaned the power distribution center. Fuse/relay box. No joy!
Replaced the ignition switch. (Because of blower Issue)
No change at all after any of these potential repairs.
Truck runs/drives great. No other mechanical, or electrical issues, Except Airbag light is always on. But I will deal with that later unless you think they are related.
Now for the weird part. Daytime (no lights on) when brake is depressed the instrument panel displays "lamp out". Overhead display reads "left rear turn lamp out", and of course it dings.
Flashers work fine, and no display unless brake is depressed.
At night: With lights on (Running lights, and, or Head lights w/running lights) right blinker makes dinging, front display reads lamp out, and overhead reads "right front turn lamp out". It flashes so fast on overhead I cannot hardly read it. If left blinker is applied nothing happen (It works fine, with no ding, and no display) If brake is applied with right blinker on it stops flashing and dings once until brake is released.
More weirdness; If left blinker is applied no ding or display even if brake is applied.
Though all of this is going on inside with dinger, and displays the right Upper stop light bulb is the only one not working. Also, the upper bulb is both brake, and flasher, but flasher works brake light does not.
Almost forgot, I did use a test light on wire to that bulb. With brakes applied no voltage. With blinker on I get voltage. Tested both at the tail light, and where it comes out of the IPM. Brown wire w/red stripe.

I really hope you can help me.
Thank you!
Tim

6 Replies

CARADIODOC

MECHANIC
33,916 POSTS

Everything you described is typical of a bad ground wire on the right rear socket. It is not totally open. It sounds like it has high resistance which is common with a partially-corroded ground connection. This is also common when Scotch-Lok connectors are used to splice in a trailer harness. Those do not seal out moisture and the wires will corrode. That can happen to feed wires too.

Turn signal functions often appear to work when the brake light function does not because current tries to go through the right bulb, cannot find a return path through the normal ground wire, but it goes over to the same filament on the other side, then doubles back through the second filament in the left bulb, and then to ground. The additional resistance of the two extra filaments causes current flow to drop to the point it might be detected as a burned-out bulb.

The best clue to see if I am right is to turn on the right turn signal, then while it is flashing, remove the left rear bulb. If the right one stops flashing, you have a ground issue. Before you remove the left bulb, you will probably be able to see the two filaments glowing very dimly if you look closely.

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Friday, December 15th, 2017 AT 12:26 PM

DODGEMAN72

MEMBER
3 POSTS

Thank You Caradiodoc!
I nad thought of grounds, but. Well anyway.
Turns out there was a bad connection in right front marker/blinker, That only fixed the blinker ding, and overhead display.
Investigation into rear wiring led to something interesting. Apparently someone (previous owner or Mechanic) had wired the left upper rear bulb in with the trailer plugs left blinker.
Disconnected that. Now NO DINGING AT ALL, no display saying lamp out. THANK GOODNESS!
However. Now both rear upper brake lights do not light up. But they still work with blinker. Just not with brake. The middle bulb still lights when brake is pressed.
I did test the wires, both at tail light, and at ICM(fuse box). That would be the white w/green, and the Brown w/red. Both have voltage with blinker (blinking), and no voltage with brake depression.
Any ideas to fix this would be greatly appreciated.

Thanks, TIM

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Sunday, December 17th, 2017 AT 2:02 PM

CARADIODOC

MECHANIC
33,916 POSTS

I suspect you're going to have a defective signal switch or wire going to it. Fortunately you still have the simple, reliable, common sense circuit that uses the same bulb for brake lights and signal lights. That means if the signal light works, that bulb, its ground wire, and more importantly, the feed wire going to it are okay.

Go to the electrical connector on the back of the signal switch and look for the white / tan wire. That one has just left a three-way splice. The second wire goes to the trailer brake controller and the third one goes to the two high-mount brakes lights. If the high-mount brake lights work, we know everything is okay up to that splice, including the brake light switch.

The left rear brake / signal wire is the dark green / red wire, and we know everything past that point is good because that's what sends the 12 volts to the rear for the left signal light. With the signal switch released, and the brake pedal pushed, you should find 12 volts on the white / tan wire at the signal switch and it should come out on the dark green / red wire. If you have the first one but not the second one, the switch is bad.

Now to complicate the story, there are actually three switch contacts involved in passing current through the signal switch for the brake lights. One switch is strictly to move the left rear wire between the signal function and everything else. The next one is the counterpart for the right rear light. If either of those were bad, only its one rear light would not work. It isn't likely you have both of those failed at the same time. The third switch moves both rear bulbs from the brake switch feed to the hazard flasher feed. That single contact affects both rear bulbs at the same time and is the obvious suspect. You might get the brake lights to work by monkeying with the hazard switch.

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Sunday, December 17th, 2017 AT 4:21 PM

DODGEMAN72

MEMBER
3 POSTS

O.K. First I'd like to say how much I really appreciate your help. I'm working 7/12's, 150 miles from home so I have very little time to figure this out.
Now, I tried to check like you said, but my truck doesn't have the same colors as you described.
My signal switch has a white w/violet, a violet w/orange, an violet w/brown, and and plain violet.
I ran out of time to check voltages and such.
This is the first time I've been under the dash. I found the remnants of an aftermarket alarm. I don't know about alarms, but I wonder if they spliced into something that is causing this (now that it is not opperational).

Now. Is there any where I can purchase a complete wiring diagram of this truck?

Thanks again, Tim

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Monday, December 18th, 2017 AT 6:53 PM