7-Pin connector not getting left turn/brake signal power

Good morning, folks.

I have a 2011 Tundra CM with factory tow package. My trailer left turn signal recently died. After replacing the bulb didn't fix the problem, I tracked down the problem to the 7-pin plug on my Tundra. With my brakes applied or flashers on, the right brake light terminal is getting 12V, but the left is not. All my truck's lights and signals work fine. I first checked all the related fuses, then just went ahead and checked every fuse under the dash and under the hood and they are all good. Any ideas on how to track this down?

I'm afraid that the only way to address is to start tracing wires, but I'm hoping there's a better way.

Thanks!

 

grab your volt meter and see if you are getting power at the plug for the L Turn/Stop

 

Whenever I have had an issue with just one function of a trailer light system, it has always been corrosion either on the truck side or the trailer side of the plugs. If there is any crud or that bluish oxidation in either of the plugs it can cause issues.

 

Thanks, folks. I did scotchbrite the terminals, so they are nice and clean. I also should have been clear about my testing: I did put a meter on the terminals and am getting power everywhere I should except the left turn/stop. The weird thing is that I just went out to do it all again now and had 12V at the left turn/stop briefly, then it disappeared again. Then it stayed dead through 20 minutes of various testing, then it came back again briefly. But if I plug the trailer in right away, I get nothing.

Seems more and more like a break somewhere.

 

reach under the bumper and push the wiring loom for the 7 pin towards the back of the truck.

 

Jiggled away with no luck. I removed the plug from the backside of the connector and checked the appropriate terminal and got nothing. So the problem is further back than that.

I have to tow our camper next week and likely won't have time to track down this problem before then, so I may need to jury-rig a jumper wire from the left rear blinker to the appropriate terminal in the 7-pin socket just to get it working for now.

 

Update on this: I used some bullet connectors and made a removable jumper from the left signal hot wire to the left turn/stop pin in my 7-pin plug. Then as I was pulling the camper home from storage, a nice guy pulls up next to me to tell me my left brake is out. Doh! Forgot that brake light power to my left side also goes through that pin. I'll pull out my lens assembly again today and tie the left brake to the left signal wire with a diode to prevent backflow. Aside from the removable ones, I soldered all connections and heat shrink wrapped them to make them pretty and factory-looking... just in case this turns into the permanent fix.

Maybe one of these days when the truck is up on the rack at my buddy's shop for an oil change, I'll spend some time tracing the wiring. Until then, this will work fine.

 

When you had the back of the plug off, did you check for voltage?

 

I did -- no voltage. The problem is further back in the wiring somewhere.

 

Last update in case this helps someone in the future. I ran a feeder from the left brake light to the jumper wire I made earlier. At the head of both of them, I soldered in diodes to ensure no electricity is backfed, i.e., hitting the brakes doesn't light up the left turn signal and turning on the left signal doesn't light up the left brake light.

Here's a pic before I zip-tied everything together nice and neat.