Turn signal woes

Hi there, new to the forum but have been a long time reader! Have an 09 Tundra Crew, 5.7L that just rolled 250k. Love the truck but having an electrical issue I can’t seem to sort out.

my left rear turn signal is not working. I’ve replaced the bulb, the socket, the entire tail light and 30” wiring pigtail that connects from the tail light to under the rear bumper as well as the turn signal fuse with no luck.

the only way I can get my left rear turn signal bulb to light is if I tap the yellow trailer wire harness but that only works once and then stops the next time I turn the truck on.

I don’t think the turn bulb is getting power for whatever reason so my next step is to tap a new wire from the flasher relay under the dash all the way back. Not sure which wire that would be though. I couldn’t make sense of the wiring diagram sticky (colors don’t match my truck).

any thoughts or suggestions? Gonna get cold here soon and am tired of using hand signals for left turns

thank you kindly,
Blue09trd

*and yes, I flushed the blinker fluid just last week, full synthetic 1000

 

Have you considered the turn signal switch itself?

 

I'm wondering if you are getting signal through the tow harness. Can you meter the socket for power with the signal switch on?

 

I haven’t considered that. As in there’s a switch behind the lever on the steering wheel? Good idea, I’ll try that and report back

 

I get an odd varying voltage when I meter it … nothing remotely close to 12V. I believe it was a decimal value below 1V (ie 0.xxx Volts). Sounds like my switch is faulty? I’ll try to compare to the passenger side that’s operable … maybe that will clue me in a bit

 

Additional context, no flashing light in that location via the hazard switch either. I’m assuming that’s a separate circuit so maybe it’s not the switch? Still worth a shot (just ordered to try)

All other lights work. Truck is stock. No LEDs or anything fancy.

 

So to be clear, your left front turn signal is working, the left side mirror turn signal ( I think you have that) is also working. Only the left REAR is inop. Correct?

 

That’s correct (Ericsopa). All other lights are working and blinking including the front left turn signal and left mirror.

The rear left signal works if I power it off the 7 pin trailer thing with a jumper wire, but then stops again after I cycle the key … I think it has to be power related, right?

New turn signal switch comes Sunday

 

As long as one of your left turn signals is flashing, then it seems like your turn signal switch (up by the steering wheel is working) and something has gone wrong in or after your turn signal relay box.... which is under the driver's side dash.
I messed with the relay flasher box on both my 2003 Tacoma and 2008 Tundra (changed current sense resistors after I installed LED turn signals) so I am somewhat familiar with its operation. Current for all left turn signal lights go through one resistor and all right turn signal light current go through the other resistor. The flasher circuit looks for a drop in current (the voltage drop across the current sense resistors goes lower) to know that only one of two turn signals is flashing (one is burnt out) so it should hyper flash. This is why I say if any left turn signal is working then the turn signal switch is working.
I don't have a picture of the turn signal flasher relay box complete, but I have one with the cover off after I replaced the current sense resistors. On my 2008 it is fairly far left on the driver's side and take a little reach under the dash to get to it.

 

Thanks for the ideas! I tried a replacement hazard/flasher box as well as a turn signal (steering wheel mounted) replacement switch today. Still no luck…. I’m at a loss . Must be a short in the wiring somewhere. Truck does have some miles on it … my buddy who’s an electrical wizard is gonna come take a look. Either that or I’m gonna have to run a new power lead from somewhere. If anyone knows where I could possibly tap that would be great. The 7 wire trailer harness doesn’t seem like the best solution but it’s a possibility I suppose.

 

Just to close the loop, finally got it figured out. Found some damaged insulation under the bed of the truck. Couple butt splices and problem solved. Good lesson to always start simple… thanks again!