left turn signal and brake light not working on trailer

[island5278]

My left turn signal and left brake light are not working on my trailer. Everything else - both running lights, right brake, right signal, works. I've eliminated everything on the trailer. If I use a light tester to test the plug on the truck side (Jeep Cherokee 2001), everything seems fine and I have a signal on the yellow wire when I'm supposed to. If I then plug it into the trailer and retest with the light tester, I get a very, very dim response from the turn signal with the light tester. If I swap wires - connect yellow truck to green trailer and green truck to yellow trailer, the problem moves with the swap. So that shows my trailer wiring and lights and I assume ground must all be good.

My blinkers are not running fast when I connect to the trailer. I've seen that mentioned as a fairly common symptom.

I'm thinking it's either the vehicle flasher or the converter. Does the flasher have anything at all to do with the brake light? If not, then I'm guessing it's the converter.

Just to be sure, I also eliminated the connector by bypassing it.

Any ideas? I've spent a lot of time to get this far.

 

[Seon]

Re: left turn signal and brake light not working on trailer

Check to see if you're getting 12V on the yellow wire at the light bulb. You probably have a break in that wire somewhere from the connector to the light bulb.

 

[island5278]

Re: left turn signal and brake light not working on trailer

It doesn't seem like it can be on the trailer. When I swap the green and yellow wires at the connector, the problem moves to the other side of the trailer. This shows that my left side light and wiring are OK.

Check to see if you're getting 12V on the yellow wire at the light bulb. You probably have a break in that wire somewhere from the connector to the light bulb.

 

[2 Eagles]

Re: left turn signal and brake light not working on trailer

I would say that your connector on the truck side is bad on the yellow wire. Try cleaning it. Or you may have to repalce the connector.

 

[island5278]

Re: left turn signal and brake light not working on trailer

I suspected the same thing, so I cut the connector out and wired the trailer directly to the truck - same behavior.

I would say that your connector on the truck side is bad on the yellow wire. Try cleaning it. Or you may have to repalce the connector.

 

[bruceb58]

Re: left turn signal and brake light not working on trailer

Did you measure the voltage at the truck side with a meter?

Also, depending on the truck, you may have a fuse for both sides.

 

[sublauxation]

Re: left turn signal and brake light not working on trailer

My Fords have all had separate fuses for left vs right. I found this out after an hour with a test light and lots of swearing, then finally looked at the owners manual for the fuses.

 

[SwampThing]

Re: left turn signal and brake light not working on trailer

Is this a new vehicle + trailer set up? Did you ever have it where all the lighting worked properly? If the first answer is yes and the second is no, then consult the owners manual for your Cherokee. Many vehicles require additional wiring and / or components for the trailer wiring to work properly due to the computer controls of the vehicle in question. The days of just crimping into the tail light harness are long gone.

My Dodge minivan requires a $250 dealer only jumper harness in order for the trailer lights to work properly. My Van is a 2000 year model. This jumper harness is an absolute mess. It requires you to remove the tail lamps, unplug the electrical plugs for the lamps, install a jumper connection on each side of the car, and then run the harness behind the rear trim panels and out to the trailer hitch. At the connection behind each tail lamp the new harness contains about 6 different relays on each side. No trailer lights will work properly without this pricey harness. Thankfully I was given one by someone who sold their van.

I also know my neighbors Yukon won't work properly without a pricey dealer only mod as well. Most people give up and just get their speech ready for when and if they do get stopped by law enforcement.

Good Luck.

 

[island5278]

Re: left turn signal and brake light not working on trailer

Not a new vehicle. Worked fine for years before this. Someone mentioned fuses. Thanks. I checked the manual and learned there is a "trailer tow" fuse. It looked fine, but I changed it anyway. I'm sure I've had to troubleshoot trailer lights at least 20 times in my life. This one really has me stumped.

Is this a new vehicle + trailer set up? Did you ever have it where all the lighting worked properly? If the first answer is yes and the second is no, then consult the owners manual for your Cherokee. Many vehicles require additional wiring and / or components for the trailer wiring to work properly due to the computer controls of the vehicle in question. The days of just crimping into the tail light harness are long gone.

My Dodge minivan requires a $250 dealer only jumper harness in order for the trailer lights to work properly. My Van is a 2000 year model. This jumper harness is an absolute mess. It requires you to remove the tail lamps, unplug the electrical plugs for the lamps, install a jumper connection on each side of the car, and then run the harness behind the rear trim panels and out to the trailer hitch. At the connection behind each tail lamp the new harness contains about 6 different relays on each side. No trailer lights will work properly without this pricey harness. Thankfully I was given one by someone who sold their van.

I also know my neighbors Yukon won't work properly without a pricey dealer only mod as well. Most people give up and just get their speech ready for when and if they do get stopped by law enforcement.

Good Luck.

 

['78 Crusader]

Re: left turn signal and brake light not working on trailer

Well? Did the fuse fix your problem?

 

[island5278]

Re: left turn signal and brake light not working on trailer

No.

Well? Did the fuse fix your problem?

 

['78 Crusader]

Re: left turn signal and brake light not working on trailer

I may have asked this question already....have you connected another vehicle to the trailer to verify it's not the trailer?

 

[island5278]

Re: left turn signal and brake light not working on trailer

No. I unfortunately don't have easy access to another vehicle. I think by swapping the left (yellow) and right (green) wires at the truck and seeing the problem switch sides on the trailer, it points at the truck.

I may have asked this question already....have you connected another vehicle to the trailer to verify it's not the trailer?

 

[bruceb58]

Re: left turn signal and brake light not working on trailer

The fact that when you used your tester and it seemed to work and then retested with a tester with a light and the light was dim tells me that you have a resistive connection somewhere on your truck. You need to trace the wire to see where it goes and test along the way.

 

[island5278]

Re: left turn signal and brake light not working on trailer

Fixed. I attached it to another trailer and it still had the left side problems. I then redid the ground on the truck's converter box, and then my light testing of the truck's plug was consistent with what I saw on the trailer - nothing from the left side yellow wire. I replaced the converter, then everything looked good on the truck plug, but amazingly, my running lights stopped working on the trailer, despite everything else looking good. Long story short - this turned out to be a ground problem. I have a tilt trailer, it turned out that I was unable to get a ground past the trailer's break point. The solution was to run ground wires from the lights to the front of the trailer. Everything now works. At one point during all of this fun, the behavior changed when I didn't even change anything. It turned out to be the ground at the trailer ball. The difference was my first tests were done when it was a little wet out, and the ball was wet and made a better contact. When the weather dried, I had completely different behavior. A wire brush on the ball solved this problem. So in total I guess I had a bad converter, no ground past the trailer tilt point, and intermittent ground initially at the ball. Oh yeah, and one time when I changed a light bulb on the trailer my truck's clock would blink when I put the right turn signal on. A turn of the bulb fixed this. Thanks for the suggestions and advice given here. What a pain this all was!

 

['78 Crusader]

Re: left turn signal and brake light not working on trailer

Great news!! Ya, bad grounds will drive you crazy and will cause all sorts of problems i.e. Gremlins.