Truck/Trailer 7-Pin Issues

Tundra is pretty new to me. Been towing with my Tacoma for years. Tundra came all set up for towing. I hooked the Tundra up to my trailer this spring, and everything worked except for the driver side blinker.

So I cleaned everything. 7 pin (both truck and trailer), trailer main ground wire. Trailer light sockets. Now nothing works. My brake controller even says "no trailer connected". But I bought a 7 pin tester, and everything on it works when I plug it into my truck.

When I hook my old truck (Tacoma ) up to my trailer, everything works. Well, passenger side blinker doesn't work, but it also doesn't light up when I use the tester, so that problem is definitely the Tacoma 7 pin. But obviously both trailer blinker bulbs are ok, as is, it seems, the trailer wiring and sockets.

So...hook up new truck, everything works except driver side blinker. Clean things, nothing works. But 7 pin tester shows power to all pins. And driver side blinker still works when I hook up the Tacoma.

All I did for cleaning on the truck was spray electrical connection cleaner on the 7-pin, then add some dielectric grease. The blades look nice and clean, though there was a little white powder like you see on battery terminals on one of the blades. Nothing going on in there I'm not used to with the Tacoma, and it always worked. Though I know problems don't always show themselves visually.

Seems like the issue is on the truck 7-pin side of things, but I'd like some advice from anyone more experienced than me.

The fact that everything works when I plug the tester into my truck is throwing me off. Just one of those things that inserts into the 7-pin on the truck, and has a little light for each function - left blinker, right blinker, brakes etc. All of them work when I test the truck.

 

If the tester has LED lights you may still have a problem in the vehicle. LED lights take very little current and a resistance blocks current flow. I prefer to use one of the ice pick type testers with a bulb in the handle and wire with alligator clip opposite the pointy end.

 

Alright thanks. I'll test it with my multimeter. And I'll just plan on tracing all the 7-pin wires on the truck, check grounds and connections. If I don't see anything there maybe replace the plug for cheap(ish) insurance.

 

No, not a multimeter. That's even worse than an LED as far as sensitivity. My late Father once told me, "You can get voltage through horse piss but you're never going to see enough current flow to get the bulb lit."

Either make up a 12 volt bulb tester preferably one that matches the circuit in watts or buy a voltage probe tester.

 

Oh alright. I knew you weren't talking about a multimeter but I assumed it would work at least as well as one of those. Still a lot to learn...Well I may order one of those but in the meantime checking and cleaning connections and grounds may solve the problem.

 

What about the fuse or breaker that's on the battery side of the 7 way? Blown or tripped? If those are fine and nothing works, probably a grounding issue on the 7 way.

Yeah, get a lighted tester or cheap meter. It will save your ass. I just finished installing a 7 way and brake controller, so the wounds are still fresh lol. Check the connection between the 4 way coupling, make sure the female side actually has the metal ring that makes contact.

Also, under the hood, do you have a DRL relay? Maybe even a tow specific relay/fuse? Check that, too.

 

I remember when you were chasing that down.

I'm still getting to know this truck and what's OEM vs an add-on. There's a large fuse on a wire at the positive battery terminal. It's not blown.

I installed my brake controller on the Tacoma years ago so I don't remember the layout. Where's this fuse? What/where is the 4 way coupling?

And I had this thought then forgot...would having my DRLs disconnected possibly cause issues?

So far I've found where the trailer brake connections are under the hood, bolted to the fender. Cleaned them. Opened the cap on the positive battery cable fuse box to inspect. But since the brake controller has power, I'm thinking my issue is toward the back end of the truck. 7 pin socket, ground, tail light splice etc.

 

Fuse. May or may not have anything to do with brake controller. But it's good.



Removed, wire brushed & reinstalled these connections (were alongside the battery).



After I get out on hike I'll look into this stuff.

 

May or may not help.
Ultimate TUNDRA Wiring Diagrams Collection | Toyota Tundra Forum (tundras.com)

 

With the amount of help you've been to the members in need on this forum I suspect you aren't the lowlife prick you profess to be

 

The fuse that's hardwired on + battery cable is part of the tow package. It runs the converter behind your driver tail light. If the DRL relay is pulled then yes it could be part of the issue.

Check for taillight/running light power at the 7 way. If ground is the 7 o'clock blade, your taillights are the 11 o'clock. Check for voltage there... don't forget to turn them on via the headlights.

Your 4 ways are joined in the spare tire pic. The little black square.

Forgot to add this. Just to be safe, check the trailer and your truck for any burnt lamps, like license plate or cab 3rd stop light.

 

Thank you Sir.
Y'all get to see my nice side....

 

Thank you guys.

I'm not in the mind frame today to study wiring diagrams so I'm leaving that for a later.

I was in the mind frame for laying under the truck, doing stuff. I pulled and cleaned this. A lot of corrosion.



I cut this connection off and re-did it with fresh wire ends.



There's a ground wire going up to the body that comes out of that tangle of wires, too. I hoped to take it off and wire brush everything, but for some reason it's screwed through the body with a flathead screw through a nut...I got the whole thing to spin, but couldn't break the screw free from the nut. PB Blaster cleaned it up a bit, so I wire brushed what I could.

Doesn't seem like there's any more cleaning that'll do any good in here.



But you can probably see there's some corrosion I've been working on. All the corrosion I've found is the white/blue dust like battery terminals gets.

Here's where I'm at. After this cleaning, but doing nothing more to the trailer, I have trailer tail lights, trailer passenger blinker again. Still no driver blinker. I didn't make it to the store today to buy a circuit tester. When I do go to the store, I'll likely just buy another vehicle 7-pin socket. Can't hurt, and will likely actually solve my problem?

 

Nice work! You probably don't need a new 7 way either. You did check the lamp on the trailer side in question, yes?

You said you had a multimeter right? Or something low enough to read 12v? You could test that pin right now on the 7 way. No voltage fluctuations with the blinker? Move back to the 4 way connectors, pull them apart, and test the blinkers on the factory 4 way side. Nothing there, still? There's the culprit.

If you do have voltage at the 7 way, go test the light socket on the trailer.

 

I get the same readings with the multimeter at the 7 pin as I do at the 4 way. Tail lights hold a steady 12v, both right and left blinker jump all over but occasionally one of the numbers they hit is 12v. Which seems right, right? They're powering off & on, so they should just be quickly flashing 12v then dropping, over and over. Or no? Strange that I see no noticeable difference between the left and right blinker.


I can test again, but I remember that when I hooked the Tacoma to the trailer, the trailer driver side blinker worked. So I think the trailer is good.

 

Sounds like the truck is operating as it should, so that should be reassuring. At least you know you have voltage in the right places. When you plug the trailer into the truck, what sort of voltage do you get at the light socket on the trailer?

 

So I guess that's the next step. That and confirming that the driver side blinker does work fine when I hook up the Tacoma, just to make sure I'm not making that up. Cause it kind of throws a wrench in all this.

 

Definitely check every bulb on the trailer just to be safe, along with your truck. Make sure there isn't anywhere the circuit could be "open".

When I was having my issue, it was the taillight/running lights that had 0v, but only the passenger blinker/brake light on the trailer worked. I was pretty baffled too, since I was getting voltage at the sockets on the trailer, but nothing from the bulbs. My license plates lights, the 3rd brake light/cab light , and (1) running light on the trailer above the taillight was out.

 

Alright. So I'm likely going to be back to tracing wires in the trailer then, sounds like. I did remove, wire brush and reinstall the the trailer ground, so that's at least off the list. But yeah, trailer has clearance lights on front and back, side lights, tail lights. Wiring is pretty much all run through the camper walls, though...it daylights in a couple places inside cupboards. Good for avoiding corrosion, bad for access.

 

I hear ya, tough to chase wires behind gypsum board. But don't worry about checking any wires until you inspect the bulbs and test the volts on the socket that isn't working.

 

So here's what I know.

I bought a 12v electrical tested from an earlier post, and either I'm a moron (completely possible), or it's actually faulty. It showed nothing even on the blinker that was working. I grounded it to the bumper.

When I hook up the Tacoma, the driver side trailer blinker works. When I hook up the Tundra, it doesn't. Doesn't seem like the issue could be with the trailer.

 

Im getting something close to that as well popping up saying trailer connection problem or whatever and if I back out of it itll pop right back up. Annoying.
My trailer brake safety pin is missing so my trrailer breaks are disconnected atm. Got a new ome coming this week. Hopefully with that connected and a safety pin corretly itll go away. All lights and break lights work as they should though
Mines a 2018

 

Electrical trouble-shooting is fun...

Funny thing is, as you start to understand electronics, it really does make things easier. And there are really fun things you can do with switches etc. And trouble-shooting is fairly straightforward. But that's only when you start to understand it. I've had moments when I was working with wiring enough that I was getting some "ah hah!" moments and seeing possibilities open up...but then I'd move on to other projects and forget most of what I learned.

I'm replacing all the trailer-related wiring harnesses and connections on my truck, hoping that will take care of things. So much for trouble-shooting...

 

Got the new trailer saftey brake hookup. Installed, not sure if its worked, need to move the trailer BUT it still doesnt show trailer connected in the truck.
All lights and signals work as they should though

 

I'm sure your brake controller has a trouble shooting guide to help narrow down where to look when you have a trailer connected but the controller doesn't acknowledge it. Off the top of my head I'm not sure why, other than dirty connections, which along with grounds always seems to be the first obvious, easy thing to check.

First thing I did was clean grounds and connections. Grounds all seemed fine, but sometimes you can't tell by looking. Some of the connections had a lot of corrosion.

 

Before when hooked up I woyld get an error say trailer connection malfunction or something thereof.
I need to move the trailer to see if it wont come up again and to see if the brakes are unlocked with new saftey brake pin.
Ill move it next week before we head out of state so ill know more then if the warning pops up.
Thats the most annoying part because if you back out itll come back

 

So because when I picked up the trailer the trailer brake wires were all fucked and heated up few connectors. While cleaning them I decided to just go get a new connector cable and wire it in. Hooked up to truck all lights still working as should but still no indication of a trailer connected

 

First thing I would try is dielectric grease (worked for me). And if that didn't work I'd take it to the shop

 

Ive got some but like i said all lights work, haven't tried trailer brakes yet, it just doesnt show connected on the dash

 

Os there a fuse for the tailer brake controller? I wonder if I blew the fuse