Tow hitch wiring harness not working

Hello,

I installed a tow hitch to tow a small utility trailer on my 02 Tacoma Prerunner that previously did not have a tow package. Now I am trying to install a 4 pin wiring harness and can't get it to work properly. I bought a Kurt 55379 harness which plugs right into the existing wiring harnesses (no splicing).

Installation was straight forward (basically plug and play), but the trailer turn signals and brake lights do not work when connected to this new harness. Running lights are fine. The Tacoma lights all function properly.

I plugged one of those 4 pin testers into the new harness and it gives me the same results............running lights light the indicator, but turn signals and brake lights do not.

Then I tried disconnecting the Tacoma taillights and just had the new harness connected. At that point (with the taillights removed) the turn signals and brake lights would light the 4 pin tester.

I also tested the trailer lights with a 12volt source on each of the three power pins and all lights seemed to work properly.

Any ideas whats going on???

 

Sounds like you either have a bad ground for the converter box
Or the box is bad.
Or your aux power for the converter is not there..
Double check what you did and if it looks ok
Get another harness and box

 

The ground for the converter box tested fine. Do you know of a way to test the converter box on the bench with either a multi-meter or a power probe?

 

Funny, I'm having the same problem with my 2013 (with tow package) and a 4-pin connecter running through an adapter plugged into the hitch connector. Running lights work fine but no brake lights or turn signals. Did you find a solution?

 

Have you checked your towing fuses? Since you have the tow package the trailer plug has separate fuses from the truck lights.

 

He doesn’t have a tow package.
Installing aftermarket.

 

Better off checking your inputs etc directly on the truck.
You would almost have to make a harness and power it correctly for a bench test.
Way to much work.

The box isn’t switching from 4 bulb to 2 bulb.
If your truck work’s correct without that hooked up.
And you have good ground
And the box has aux power
And it’s plug and play.
it should work.
If not
You missed something
Or it’s defective

I’m not there
Can’t help you much more than this

 

If you have a factory tow package and going from 7 to 4 with a adapter you do have fuses in the under hood fuse box...

 

Thanks guys. I hooked up to a buddy's trailer and got the same issue so it does seem to be with the truck/adapter and not the trailer. Going to get back at this little mystery today once the auto parts store opens. I checked the fuses and they looked OK, but I'm going to try replacing them anyway and double-checking to see if there are any that I missed. Also going to try a different 7-4 adapter.

 

So I replaced every fuse I could find that seemed related to towing, and I pulled and checked every other fuse. Still no luck. Does the 2nd get have some additional third secret fuse box somewhere with towing fuses?

Also, a thought. My battery is 5 years old; could it be a weakening battery issue?

 

Something defective with the new Converter box or the 4 pin plug .

if all the truck lights were working.

 

Agreed, thanks. I've tried 2 different converters now so it's probably not that. I think I try replacing the relay next; if it's not that I hate to say it but there may be a dealer trip in my future. Need to get this fixed.

 

This thing is driving me a little cookoo!
I tried a bunch of testing today. Here are my results.........

With the trailer disconnected from the 4-pin connector and the following color coding....
White: ground
Brown: Running lights
Yellow: left turn/stop
Green: right turn/stop

the following measurements were made at the 4-pin connector:
with no lights turned on with running lights on Rt. turn signal on Lt. turn signal on
W:Ground Ground Ground Ground
B:Ground 13.7 v .2v pulsing .2v pulsing
Y:Open Open Open 12.1v pulsing
G:Open Open 12.7v pulsing open

Then I connected a pair of tail lights to the 4 pin connector. Running lights worked fine with light switch on.
Now,(with running lights turned off) if I activate rt. turn signal I get nothing but if I disconnect the Green wire (rt. signal) while rt. signal is activated, then reconnect the green wire, my rt. signal works.
I can turn right signal off then back on and it works but if I turn the left signal on then back to the right......it no longer works!!!

HELP!!!!!!

 

If all the lights work on the truck Do They??

It can only be the Converter Box or the wiring between the truck Harness and the 4 pin plug .


No matter how many converter boxes you have replaced something is still not correct.

Good Luck!!

 

All of the lights work on the truck. I have another harness on order

$53 Tekonsha T-One® T-Connector Harness, 4-Way Flat, Compatible with Select Toyota Pickup, Tacoma, Black

https://www.amazon.com/gp/product/B0012RGA2W/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8 which I should receive in a day or two. I will report back after I try that.

 

First, OP, apologies for muddling into your trailer lights thread - I certnaly didn't mean to higjack anything here, and I hope the new harness fixes your issue. But I would like to post the solution to my issue here in case future TW people search this topic and my solution can be of help.

To recap, I was using a 7-4 converter but only the tail lights on the trailer would work. No brake lights, no hazards, no turn signals. I checked every fuse, swapped relays, and even checked the tabs on the hitch harness for current. Nothing helped. So I took it to the dealer and they basically had to tear out interior panels and follow the harness underneath the truck from the firewall to the hitch. They found a few places where there was corrosion on some connectors and cleaned things up (and maybe spliced... who knows?) as needed. All is working now. Sucks that I had to spend $360 at the dealer, but I was at the end of my rope with it and out of ideas. I will say the dealer treated me well and I never felt like they were going to gouge me for the work. It was an honest 3-4 hours of their time to get it done.

 

BuddyS no problem......we're all friends here.
And YAHOO!!!!! the new harness fixed the problem for me!!!! Now it's Trumer Pils time!

 

Sweet -- Congrats!

 

Congrats. BUT. You’re telling me Toyota has a corrosion issue with the factory installed cable harness and you had to pay for them to fix their poor manufacturing. Humm. I’d write Toyota and get a refund. You may also look for a maintenance bulletin. You can also contact the federal government https://www.nhtsa.gov file a complaint. It will help us all

 

19 yo truck. Toyota can’t be held responsible for corrosion on any part after that long. Heaven only knows where that truck has been.