Trailer running lights question

B

bassarama

Junior Member
As I was replacing a coupe of lights on the trailer, I realize that my 98 Dodge Truck has no power to the running lights, I mean the wires are connected and everything looks like it was done professionally, however the 12 volt tester shows no power on the running light pins. Only the brakes and blinker lights work.

First I though the trailer wires were bad, but connecting the trailer on the Tahoe everything works fine.

I have yet to trace every piece of wire under the truck, but from what I can see so far, the wiring looks sordid and like I said it was done by a professional perhaps from the manufacturer.

I've check the fuses and every one seem ok; I'm leading toward a separate fuse and /or connector under the firewall...

Have you experienced such problem or know of any possible cause that would lead to this?


Thanks

Joe
 
If I'm not mistaken all newer vehicles need a wire harness T connector to install trailer lights. These are usually $9-$39 depending on vehicle. If someone somewhat familier with adding trailer lights on older vehicles did it to the newer models it is likely to get the results you have. Check and see if you have this T connection, look under the truck where the main wire harness in the rear along the frame and trace the wire to the trailer lights. If so other problems exist, if not get one and install it (Walmart, etc).
 
The problem that usually exists when hard wireing is the use of blinker and brake lights. NOTE that the trailer has a combo brake and blinker whereas most vehicles have a brake light and orange blinker, so a converter is needed. In some instances when the vehicle has a combo brake and blinker a converter is still needed because of the way the vehicle seeks power.
I have seen one instance where the owner did not want to purchase the T but did install the converter and still had problems, once he installed the T and harness all problems ceised.
And the possibility does exist that there may be a fuse just for trailer lights in the truck, under the dash or hood. A F150 we have has such a setup.
 
Thanks

The truck has an original towing package, so the trailer hitch and the connector plug were there form the manufacturer...which explains the way all the wiring is professionally done, ( neat work and shrink warp on each crimp)

Again, all lights on the truck work. For the towing plug, there's is only power for brakes and blinkers, not for running lights.

Joe
 
Visually check to see if all fuses are good under dash and hood by removeing one by one (so not to get confused). If you have the book (in the glove compartment) on that vehicle it will usually list each fuse location, designation and size.
Don't take it as the gospel that the towing package was installed correctly by professionals. Most of the time dealers will send their vehicles to places like U-Haul and have them installed.
If you run into an impass, just add the T connector and harness and see if that fixes the problem (cheaper and quicker).
 
Bass, I had this problem with my Jeep. With every other vehicle my park lights worked but brake and blinkers did not. I hated that crap. Now with my Yukon, everything works and I'm happy.

Sounds like a similar type of problem. I wish I knew what to tell you. Sounds like Tsub knows a little about how it all works. ;)
 
I can get into a whole speil of what it can be and still not cover the problem, but I'll throw some at you:
The primary cause of all trailer light  malfunctions is the lack (or damage) of a ground, the negative wire, (the black one on the battery) the white one at the trailer light wire harness, what ever color the manufacturer deemed correct in the wireing harness for that particular model that year. This is not to say you can derive a ground from the frame or metal part of a vehicle on newer vehicles, usually it must go thru the wire harness so as to not create other problems in the vehicle, especially ones with a body computer.
 
The green wire is the right blinker and brake light.
The yellow wire is the left blinker and brake light.
The brown wire is the running lights.
The white wire is the ground.
The fact that it works on the Tahoe was a quick analysis (good job), check and see if you get a reading between the white wire and the brown wire (with parking lights on) with a test light (not a meter) closer to the harness away from the plug to see if the plug is damaged.
The fact that the truck had wires spliced could be the whole problem also. I had one that the lights would occasionally not work until I got under the truck and wrapped my hand around the wire connections and twisted.
 
Thanks

I had a light tester at the end terminal and determined that there is no power at all coming from the wires, the terminal plug is fine, I wonder if there's an additional fuse for the running lights alone, normally one fuse covers the whole circuit right?

I need to spend more time under that truck and follow the logical path and your leads with the color code.


Gotta love all this agravation/chalange.(insert head banger HERE) >:(


Thanks guys

Joe
 
Reread this thread. I don't know about newer Dodge (I'm partial to them), but ("96 & newer) Ford does have a fuse just for the running lights under the dash with the rest of the fuses.
Those wire colors are only for the pigtail to the trailer lights,truck wire colors will not corresponde to that.
 
99 Ford F150 had fuse for trailer harness under hood in a small fuse box, Driver side close to firewall away from the big fuse box under the hood.

Had 3 fuse boxes in that truck!! so confusing!!
 
you may have answered this, but did you test without the trailer hooked up. just a test light to the female plug coming off the truck. i have a 95 dodge and will go look at something if you need me to.
 
I have checked (with a 12 V tester) the terminal connections at the round plug, no juice for the running lights. It has to be a #$%&^ fuse .

I have a hard time believing that I have a broken connection or it was wired wrong!!

Thanks

Joe
 
Do the book in the glove box thing.
If not pull and check all fuses one by one.
If no problems add new T connection and harness.
 
I have the same plug and they sell an adapter to plug right in for your 4 or 5 wire trailer plug.

When testibng the wires in the round plug make sure you are testing the right side for tail lights, the plugn on truck is in reverse!I have made this mistake before!! :-[
trailer_light.jpg
 
Trying to make this look like the 7 wire plug for Mopar and most others.
Imagine that the notch in the plug is up and you got 6 terminals around the perimeter and one in the center top.

                                  notch

                              3             4
                         
                          5         7          6

                              1             2

1 Ground (common)
2 Electric brake
3 Tail & license plate
4 Battery (aux 12v)
5 Left turn & stop
6 Right turn & stop
7 Bach-up lights
 
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