First Gen Trailer Wiring Issue

Hello all,

I've done a bunch of searching but there seems to be no other issues similar to mine. Hoping for some insight.

2004 Tacoma 3.4 Xtra cab manual 4x4.

I installed a Curt plug in trailer wiring harness a few years ago and it worked great. Recently the turn and brake signals on my trailer started working intermittently. Running lights always work. I can 100% verify it is not the trailer. When I test the turn signals with a volt meter at the 4 pin I get alternating voltage up to 10-11v. When I use a 4 pin tester on the 4 pin from the truck I only get a signal for the running lights. You would think these turn signal test lights would flash. When I turn off the running lights, the tester fires the turn signal lights but the signals don't work when hooked up to a trailer. I can verify that the tester works. Running lights are 12v when tested at the 4 pin.

I have tried harnesses from Curt, Tekonsha and Hopkins and all have the same result. I have also spliced in to the wiring directly, then to a converter to a 4 pin plug. Same result. I have also replaced the tailight assemblies thinking that the issue might be in the connections. I have run new ground wires, traced the wires best I can for any cracks etc and found nothing. Tailights on the truck work perfectly. I also have a newer battery and have replaced all fuses (that I can find) to do with lighting just to make sure.

I don't understand why I would have "proper" voltage at the truck side 4 pin plug for the turn signals, yet it won't fire the tester lights. When I hook to trailers, all brakes and signals will work, then two minutes later only one side etc. I've even called a couple of trailer shops and they say they are stumped. I have tried to track down an OEM trailer wiring harness but they are no longer made and I can't find one.

Any help is appreciated! The truck is low miles and pretty close to perfect shape so it's bothering me to not have it perfect! Plus the safety for towing...

 

for me and trailers it has always been grounding issue. I quit using the flat 4 connectors for that reason and went to the 7 pin round style. On the "problem child" rigs I have worked on the issue always seem to be people are expecting the trailer to ground to the truck through the hitch ball.

for MY200X Toyota had a issue with the convertor box and issued some documentation... if it is a waste of your time and doesn't apply, accept my apologies in advance.

 

Trailer lights are nothing but a pain in the butt. The issue can be found trouble shooting one section at a time.

I also only use 7 Pin plugs anymore eliminate those problem converter boxes.

converter box gets hot and quits poor connection gets hot enough to open then works again once it gets cool

trying to get a good ground connection through the hitch is a joke .

 

Thanks for the replies! The 7 pin I use wires from the 4 pin. I never thought of wiring it straight to the 7 pin. I will give it a go.

 

I suspect if the hitch connection is even a tad bit loose, you may also be up against an intermittent ground if that's your only one. Not ideal.

 

I thought that too but it happens on both trailers, and doesn't explain why it won't fire the 4 pin tester.

 

Sounds to me like there's an issue with the ground wire on the 4 pin tester. If you put a multimeter on to Resistance mode, then put one lead on the ground pin of the connector and one on somewhere else (like a jumper to the neg bat terminal or somewhere on the frame), what kind of resistance do you get?

 

The four pin tester works, verified on my other car and others. Here is a picture of one of the plug in harnesses I have where the vehicle end has test lights. The green lights indicate voltage is good, tester shows no signal even thought there is voltage. This is verified when I plug in the trailer since the brake and signals do not work. It makes zero sense to me. I cleaned and verified ground from the battery to frame is good and clean, and good ground on the plug end.

I need to figure out how to wire directly to a 7 pin plug but I am confused how to route the turn and brake signal to one wire. Researching now.

Many thanks for all of your input so far.

 

This happens with 3 different harnesses, so it is unlikely the connector. Same thing happens when I plug the 4 pin into my 4:7 pin adapter.

 

Sorry, I meant the ground on the 4 pin connector on the truck, not the tester itself.

 

for me it's always the converter box itself that goes bad. they aren't designed to last and it's easier to swap them out. I think I'm on my 4th or 5th in 17 years. my new one now blows the fuse for the running lights but otherwise works fine, yay Curt crap. So I bought another plug-in style to replace the whole setup to see if it's maybe the wires at the tail lights that are the issue (they are old after all).

to wire to a 7 pin, cut off the connector on the end and run the 4 wires into the 7-pin box and attach to the correct screws. ground would then go to frame or run a length back to the - on battery.

You can also add additional options at this point as well like a back up light on the trailer, or 12v hot for accessories.

 

Any Luck Figuring this out?

If you were close to me I would be Glad to help.

 

No luck yet. Thanks again to everyone for the input. I’ve had some other people check it out and everyone is perplexed. If you check vehicle side four pin you would think it would work perfectly. Was towing a trailer yesterday and turn and brakes were intermittent again. Pull over one time it works perfectly, next time no signals, next time no right signals etc etc. I have tested both the trailer and tester on other vehicles and they work perfectly.

Tried different converter boxes and multiple trailers with same result. Replaced the turn signal relay yesterday thinking it might be wonky but no change. Voltage checks at and before and after taillights is good. Ran a new ground directly to battery and no luck. The fact that the four pin tests perfectly (also as evidenced by the about picture) would point to it not being a ground issue since voltage is good.

This is especially bad timing because I’ve been considering a newer ridgeline for awhile especially because I’ve got a ton of highway driving to do in the next 6-8 months and planning on doing a bunch of towing. I will try to resist going to the dark side haha. I think I would cry when it came time to sell the old Tacoma.

 

you have cleaned both plugs ??

If the trailer plug is exposed to the weather.

I had one drove me nuts unseen corrosion yet it would check out fine with the meter

As nothing else seems to be found defective.

 

All good suggestions her. Just suspect the "bullet" connectors on the 4 pin...like Wyoming09 said, above. I clean out the holes in the plug with the fattest of my torch nozzle cleaners

 

which converters did you buy?

Try one with a dedicated 12v power source (if you haven't already) as that bypasses the need to power from the wiring circuit.

 

I have been fighting the same problem on new four flat to seven blade socket. All OK except no brake lights.

Trailer lights work fine when hooked to different vehicle.

Just checked voltage to all pins, and other blinkers plus running lights have power. No power to brake light pin.

Looked for converter box, and found it under rear jump seat in well with jack. Lines going into it are marked, so so pulled apart the brake wire connector to find a blown 5 amp fuse.

Going to town tomorrow to get a fuse.

 

nice, you had one of the OEM converters, many would like those as they are isolated from the regular wires. If I could find one online I would buy in a heartbeat

 

my problem is very similar but maybe more complex but also could shed some light on your problem. at the trailer hookup on the truck I use a pigtail with the indicator lights to trouble shoot. the right (green wire) will be hot sometimes and sometimes not. I found the best way to make it mess up and not work is the first time you turn the ignition on but not crank it and turn the right blinker on it does not work and the brake light (green wire) does not work. if I take a volt meter and check it, thats all it takes to make it start working and the light on the pig tail starts flashing. now it seems to work everytime until you shut off the ignition and blinker for a couple minutes then it may work or may not work. I even had the volt meter hooked up when I turn the ignition on and blink and every time the blinker blinked the volt meter would beep and read 1. plus volts. but its just reading the volts of the meeter everytime the blinker blinks and while I'm standing there watching the meeter all of a sudden the meter picks up 10 plus volts and the indicator light on the pig tail starts working. then again it seems to work everytime excepts when I turn the ignition and blinker off for a few minutes, I'm not saying that the only time it will do it but that the only way I have been able to replicate the problem with any regularity. it seem just the small amount of voltage in the voltmeter is all it takes to make it start working, shacking wires does absolutely nothing. the left side works everytime, even when the right is not. I had the truck running with the brake pedal down and the left light on the pigtail was working and right not, tried right blinker and nothing then it starts to work.

 

the green wire is actually only the turn signal from the right. Ground, Run, Brake, Left all come from the left connector