Trailer lights not right

Hello all. I have a 2020 Taco and pulling a small trailer for biz purposes (Custom Woodworking). Lately the trailer lights have been giving me fits. Everything on truck, tail lights, blinkers,etc, works fine. On the trailer, when I do left turn, both back lights on the trailer blink. Right turn works fine. I've tried this on 2 different trailers and same thing happens on both which tells me that its either the connector or fuses or something on the truck. My specialty is woodworking and not electronics or mechanics. I've tried figuring out the fuses but since I don't have a PhD in abbreviations, I can't figure out a lot of them. I'm hoping somebody could save me a few bucks from having to take to dealer to fix. Thanks for any advice.

 

95% of electrical trailer issues are a bad ground.

 

for starters, you need a tester.

$19 MECMO 360° Rotatable Vehicle Side Trailer Socket Tester, 7 Way Blade & 4 Pin Trailer Light Wire Circuit Tester 6 Function LED Indicators Towing Vehicle Trailer Wiring Plug Tester for RV Truck

https://www.amazon.com/MECMO-Trailer-Function-Indicators-Vehicle-Side/dp/B0C6F3F454/

this would verify that the truck-side is good. but very rarely does the truck side fail.

you're likely experiencing either a miss-wired trailer plug, intentionally or accidently(i've come across both), or a general trailer wiring problem.

the next step would be either
a. take the trailer to a mechanic, and let them sort it out
or
b. grab a good 12v battery, and jump across the individual pins on the trailer plug to verify functionality or confirm the error. once you've found that it's in the trailer wiring, identify how many wires have issues, and then visually inspect those wires from the tongue to the lights--normally, you'll find damage along the way.



you don't state your location, but if the 'indy' part is any indication, i'm up in the northern corner of indiana, if you're near by i'd be happy to try to help you troubleshoot.

 

Yup, either bad ground or the harness is shorted somewhere. Since you said you tried 2 different trailers, And I'm assuming it WAS working and nothing has been re-wired since, left blinker making both sides flash tells me the left blinker circuit is shorting to the tail light circuit. The fact that it's doing *something* tells me the fuses are good. Are they flashing dimly like tail lights? or brightly like your flashers are on?

Also, are you using an adapter to go from 4pin to 7pin? maybe the adapter is bad. water or corrosion inside could cause power to bleed over where you don't want it

An adaptor/test plug with indicator LEDs and/or basic $10 multimeter will tell you where the failure is. Test each function at the truck's plug and make sure the wrong pins aren't getting power for each one. Just be careful not to short any of the trucks pins to the ground pin, or you'll be chasing your tail a while before you find out you've popped fuses

If the truck tests good, and you've tried 2 separate trailers with identical malfunctions, it's gotta be the adaptor you're using. To verify that, switch the multimeter to continuity/ohms mode and check that you have NO continuity between any of the pins on each side. I wager you'll find that pins 5 and 3 (which happen to be adjacent) are talking to each other when they shouldn't be.

 

Great suggestions. Appreciate all the advice. Same thing is happening on seperate trailers so I know its not the trailer. There is some light on so would think it rules out fuse. Must be short in the plug. Will try that first. Thanks for responses!

 

After you get it working. Use that dielectric grease and coat the hell out of your plugins and adapters. Never knew how much it can save you trouble in the long run, especially off-roading and dusty roads.

Good luck on the fix, electrical is annoying.

 

Thanks wisky57. I did use it when I first got it a few years back. Probably should have reapplied more often. Will definitely do so in future. Thanks

 

Not a problem. It's a life saver. I always yell at people at work when they don't keep using it. Simple but effective.