Trailer 4-pin problem

Alrighty, I've officially exhausted the slim extent of my electrical knowledge trying to figure this out, so please, God's of the Tacoma world, help a brother out lol. I had a 4 pin connector when I purchased the truck (used, very lightly) and the connector didn't work from the get go but never needed it till now. I replaced the existing wiring, T-connectors, and converter box behind the drivers side tail light. Now that box had a wire that ran to the battery with an inline fuse. The tekonsha T-connector and converter box I bought did not have that wire to the battery and was not damaged when I received or opened the packaging, so I can assume that there is nothing wrong with the unit. I hooked everything up, grounded the unit and my tail lights work, so power is going through the unit to get from the harness to the lights, but the 4-pin doesn't work. I'm at a loss.

 

Your old converter was powered- it uses the red wire to power all the trailer lights, and the factory wiring just provides the signal to tell the box what to activate. It protects the truck wiring from you hooking up a trailer with a short circuit (a good idea) and makes it so the factory wiring isn't carrying any extra load (not so necessary). Your new one pretty much makes the trailer light circuits an extension of the truck's light circuits.

When you say the 4-pin doesn't work, what exactly do you mean, and how did you reach that conclusion? Are you checking with a trailer? A 4-pin plug in tester? A multimeter? Do any of the functions work, or no? If you're sure there's no output, my 1st guess is that it's got a ground connection, and it isn't grounded well enough. Is there a separate ground connection, or is it 100% through the T-harness? My 1st gen had a converter box, and while they could've grounded through the T-harness, I seem to recall that it did have a separate ground...

 

It did have a separate ground that has been connected to the available ground point behind the drivers side tail light. As far as how I tested it, I used a set of trailer lights.

 

Do you have a multimeter? Know how to use it? Rather than checking with trailer lights, I'd grab a meter and start checking stuff. Check resistance from your ground wire to a ground in the taillight harness. Check and see if you're getting any voltage on your any of your 4-pin outputs.

<---- guy who has had several "derrrrrp" moments due to making assumptions about things in testing processes.

 

That's a negative ghost rider, but I can get ove to use for a day.

 

Extech meters are decent (not great, but they don't need to be for most automotive uses) and can be had cheap. It'll pay for itself the 1st hour (or maybe even half) of shop diag you don't pay.

The converter boxes do fail obviously (I think I went through 4 on my old truck in 14 years) but I wouldn't think it'd be DOA right out of the box. Could be, but more likely you've got an issue somewhere else. Pretty freakin' unlikely that problem is in your harness plugs, so I think it almost has to be that ground. For a fun test, hook up a trailer and drive down a bumpy road, see if the lights flicker as it tries to get a good ground through the ball & hitch!

 

I'll be sure to give the meter a try, thank you!!

 

Let me pass on a few words of advice from the Service Manager at the marina where I work. "Most stupid electrical problems are the result of a bad ground." Damned if he hasn't been right with that one many, many times. When you get your DVM, check the simple stuff (like the ground) first.

 

Here's another question. In the fuse box under the hood, there are 3 "towing" fuse locations if I remember, one of which is a relay looking box type fuse (my apologies for the terrible description). One of them says "towing tail", the others just say towing. None of them had fuses in them when I bought the truck. So should I throw fuses in there or are they not necessary with the T-connector that I am currently using?

 

This is where that DVM will help. If you have no power coming out, I'd say the fuses might help.

 

Awesome, thank you!

 

NEVER EVER NEVER EVER NEVER EVER
use a trailers lights to diagnose a problem.


I have rewired a trailer only to have it act up in 3 months. I have had every sort of trailer light issue imaginable. So much so that I have magnetic tow lights that stay indoors and are my go to solution for small trailers. They work 100% of the time. Never trust trailer lights as your testing method.

I also carry plug in testers in my truck to test my truck wiring any time I have any question about where the issue is truck or trailer.

I can’t comment on Toyota’s but Dodge trucks had an issue in the main fuse / relay box where the trailer flasher relay is. You might own the truck for a decade and the first time you hooked a trailer up the signals wouldn’t work. The relay works everytime you turn the signals on with or without a trailer. It burns up and it is an $800+ fix. I used one of those powered tail light converters like mentioned above. The problem with them is not enough current and the box won’t trigger. Other times it will trigger a bulb out light on the dash. So yes powered tail light converter boxes are a cheap fix to getting trailer lights but they can be unreliable. I was able to sort my dodge problems with one only because the other option was $700 more.

 

Those should be for factory tow wiring. A T-harness gets its power from the truck lights, or a whole separate circuit if it's a powered one like the one you removed.

 

Now see, I don't have the factory tow package. And the one I removed didn't work anyway. So the one that I just put in SHOULD be working, I still can't figure out why it's not, it doesn't make sense.

 

So update, it was a ground problem. It would appear that the ground post behind the driversd side tail light is kaput, so I ran the wire down to the receiver frame and put a self tapper thrpigh her and KERPLOW, it worked like a charm. And the day after it gets fixed, I end up needing to tow a saab from PA to NY, roughly 120 miles one way. The Tacoma took it like a champ.

 

Ah, so our Service manager was right! Congratulations!