Trailer Lights Gurus--Got a Question.

[mbsimpson99]

With a 4pin connector the taillights and signal lines are only energized when the vehicle's are.

Whatever the vehicle behavior is will be what your lights are: so if your vehicle has no markers unless the headlights are on, the same goes for the trailer

I agree this is how they should work. I had a similar issue on my Ford Excursion. I had turn signals but no taillights. Only had 8-9 volts at connector. Checked ground, jumpered a temporary ground still no luck. Fuses checked good. Found a fuse for trailer tow relay. It checked good but in the process of removing and replacing fuse the connector read 12 volts. Couldn’t get it to stay on but looks like it is due to bad contact in the fuse holder. The 7 blade connector reads good so I am going to swap in a new 7 blade with a 4 blade built into it. Hopefully that will bypass the bad 4 pin wiring.

 

[Dmacleo]

So, I'm curious why npalen needs his trailer lights on without his tow vehicle lights on.

yeah I missed a lot in this long thread but iirc NO lights (brake/turn) worked w/o the light switch being on.

in the many pages I did not see vehicle make/model.
from approx 2008 on gmc truck trailer lights controlled by a Trailer Lamp Control Module usually mounted by spare tire. if it does not have that all triler lighting controlled by the body control module.
many fords control this off the LCM (light control module) for my 2010 marquis had to buy a Circuit Protected ModuLite such as this:

https://www.etrailer.com/Wiring/Mercury/Grand+Marquis/2010/119179KIT.html?VehicleID=20101174601

places like etrailer have kits for this.
my kit (can't find link for) kit required a circuit breaker protected power (linked one is a 10A fuse is updated version of what I got) off battery, that provides power to the lights depending on what the LCM sends out as signal.
I then plugged the 4 pin output into this:

https://www.etrailer.com/Wiring/Tow_Ready/30717.html

to give me 7 pin which I then wired trailer brake module (aftermarket) into as well as full time power for breakaway battery charging and I also hooked relay up to my reverse light (rev light only used as signal) and used those incoming 40A wires to power reverse light under bumper as well as 4 led reverse lights on trailer.

point I am trying to make is you can no longer just splice the 4 wires onto the wires at tail light end.

 

[WranglerX]

Many Fords do not have a flasher unit. My '08 F350 turn signals are controlled by the ECM. Found that out when I went to install LED's. Have to use external resistors on all four corners, but that also compensates for LED trailer lights.

Yes!...

 

[npalen]

Do brake lights still work with ignition off?

Bruce

Bruce--I think I checked that and they do work but will double check.

 

[bigwave]

Hi NPALEN, back at entry number 76 you posted a picture of wiring that I presume came from ad, look at bottom example where it shows 3 wires coming out of fixture, if fixture only has 2 wires it doesn't have both tail & brake / turn light functions, they either gave you a bad set of fixtures or you got ONLY tail or brake / turn function fixtures; not both. the 2 wires; either brown / yellow or brown / green coming back can't be hooked together. if you can open fixture look and see if there's a third wire maybe tucked inside. There are dim and bright LED's for the 2 functions. Hope this helps,

 

[Doughknob]

Who is his grampa?

He IS?

 

[npalen]

He IS?

Oh, I get it. His Grampa is He. I suppose He has a brother named Haw. (Who would perhaps be a great uncle to Who)

 

[NCL4701]

Apologize if this has been said as I haven’t read every word of this thread.

I have a friend with a late model Jeep Cherokee he uses to tow a boat trailer with a 5 pin flat plug. He had the exact same problem. We hooked it to my Tundra and the trailer lights worked normally. He contacted the dealership and they told him that’s how the lights work on his Jeep. Never heard of such but now he just knows he has to turn on at least the parking lights whenever he’s towing.

 

[ForestGrump]

Normally trailer lights are connected to the vehicle lights. How else would your turn signals and brake lights work?

 

[CausticUrbanCoast]

Normally trailer lights are connected to the vehicle lights. How else would your turn signals and brake lights work?

Depends if your vehicle has a towing package or not, if so they may not be tapped into the lighting harness.

 

[Tony H]

Bear in mind again that there is no power to the 4pin trailer connector UNLESS the pickup lights are ON. The trailer lights all work perfectly then.
Nothing can work if there is no power. The issue has to be in the pickup wiring, right?

If you put a meter on the ground pin on the truck connector and the other meter lead to another socket (green or yellow wire)on same connector, will you get voltage on the meter when stepping on brakes? That will let you know that truck wiring is correct to that connector

 

[npalen]

If you put a meter on the ground pin on the truck connector and the other meter lead to another socket (green or yellow wire)on same connector, will you get voltage on the meter when stepping on brakes? That will let you know that truck wiring is correct to that connector

I don't blame you for not reading through all the posts of this long thread but the problem, which was operator error on my part, has been solved. Thanks.

 

[npalen]

Having said that it has been solved, I did notice today that the brakelight function is not working for some reason. Works on the pickup but not the trailer. All the other trailer light functions seem to work fine..

I don't blame you for not reading through all the posts of this long thread but the problem, which was operator error on my part, has been solved. Thanks.

 

[WranglerX]

Gads hope this tread doesn't go on to 202 pages like rounded off drain plug thread....

 

[npalen]

Gads hope this tread doesn't go on to 202 pages like rounded off drain plug thread....

HaHa It ain't over till its over.
So why wouldn't the d**n brake light work when everything else does?

 

[Midniteoyl]

HaHa It ain't over till its over.
So why wouldn't the d**n brake light work when everything else does?

Your wire colors were incorrect so maybe you have the the 'brake/turn' wires of the LEDs actually hooked to the running light wire?

 

[npalen]

I wondered about that so switched them and didn't make any difference. Should see a light either way though when the brake is depressed. Right?

I do understand that the lights wouldn't be as bright if they were wired backwards since only the "tail light LED's would be lighting when brake is depressed.

Will investigate further to see if I'm getting any voltage at the trailer light connector when brake is depressed. (probably not)

 

[Midniteoyl]

I wondered about that so switched them and didn't make any difference. Should see a light either way though when the brake is depressed. Right?

I do understand that the lights wouldn't be as bright if they were wired backwards since only the "tail light LED's would be lighting when brake is depressed.

Will investigate further to see if I'm getting any voltage at the trailer light connector when brake is depressed. (probably not)

Might also need to add a resistor like shown earlier in the thread.

 

[WranglerX]

Check connector on truck first.... If its good, then trouble shoot trailer... IF brake pedal pressed you should have 12volts at yellow and green wires at plug on truck...

IF turn signals work at trailer the trailer wiring is good.... IF you take small 12 volt battery (battery charger or jump box) and a clip cord to connect trailer plug ground wire to minus (-) side of battery supply and use another clip cord to put 12 volts from battery plus(+) to each of the corresponding wires (yellow/green/brown) and proper LEDS illuminate on trailer, all your problems are in truck....

At trailed plug using just a 12volt battery (or battery charger)
put ground on trailer white wire
put 12 volts on brown wire, tail lights ( and side markers if equipped) come on.
put 12 volts on green wire bright LED for RIGHT side stop/turn comes on.
put 12 volts on yellow wire bright LED for LEFT side stop/turn comes on.

If you get these results your trailer wiring is good..... PERIOD...

Also find this tool for trouble shooting best ever.... Lamp "on" you have both voltage and ground.. Lamp off, either voltage or ground or both missing...

Just to be clear I have 4 multimeters, 2 analog and 2 digital, and this $5-10 tool is preferred for automotive wiring trouble shooting (non computer circuits) ...

And yes I do get deep wiring, this is a in process picture of developing a full wiring harness for VW DUNE BUGGY with all full road legal wiring for lights and engine instrumentation...

And done,,,

 

[aczlan]

Might also need to add a resistor like shown earlier in the thread.

Shouldn't need one, I would bet lunch on it being a wiring problem.

Aaron Z