Trailer light problem

L

lloyds

New member
Have question for those really familiar with trailer light wiring. I have a 7 pin plug on truck. Tested pins and starting from bottom and going clockwise pin 1 is blank, pin 2 is left turn, pin 3 is blank, pin 4 is head and tail lights, pins 5 and 6 are blank. When I turn on the truck pin 4 is energized and also is energized when I turn on the headlights. So when I hook up to the boat everything works properly, but when I hook up to the rv i have no taillights. Did the same test on the rv plug and the results where the same as with the trucks but the trailer tail lights do not come on when I turn on the key or when I turn on the headlights. Any ideas?

Correction: Pin 5 is right turn
 
Your pin #4 (top right) is absolutely for the tail lights. In all my experiences with trailers, the first thing I always check is that there is a good ground. I've chased stuff for hours to only find the trailer had an iffy ground. The stuff you say is blank probably isn't....going from memory if I remember anything from working at the RV dealership once upon a time this is the common set up: Your order....

#1 is trailer brakes
#2 is RT and brake lights
#3 is 12v charge for your battery
#4 is tail lights
#5 is LT and brake lights
#6 is the ground
#7 (middle) is reverse lights
 
Thanks for the reply. Mine is as you describe except left and right turn signals are reversed. Still don't understand how pin 4 on the rv can be energized but still no taillights but same situation while hooked to the truck and they don't light. Maybe something wrong with the interconnect with the pin 4 on the rv.
 
These photos may help some.

This first photo is of the inside of the 7 pin trailer plug. (You'd be looking at the back side of the plug where the wires attach.)
TrailerPlugInside.jpg
TM Tail Marker, AX Auxiliary (12vt), LT Left Turn, RT Right Turn, GD Ground, BU Backup, EB Electric Brakes

Trailer_Wiring_Color_Code.sized.jpg

Also, on the newer Ford trucks with the factory tow package, some of the pins will not operate until the truck's computer recognizes an attached trailer. In which case, the pins would be unenergized while checking with a VOM but no trailer pigtail attached. Colby
 
lloyds":1iwbfqr4 said:
Thanks for the reply. Mine is as you describe except left and right turn signals are reversed. Still don't understand how pin 4 on the rv can be energized but still no taillights but same situation while hooked to the truck and they don't light. Maybe something wrong with the interconnect with the pin 4 on the rv.
Click to expand...

Yup got them backwards. I'm sorry - I should have looked it up....It has to be something simple....bad connection or terminal....no ground....something like it. It might even be bad bulbs. I always check the cheap and easy stuff first.
 
checked all that. Everything works on truck and on rv except the taillights on the rv. Have another male 7 pin so going to try that. the last illustration is how my plug is configured.
 
I'm assuming when you talk about your truck and your RV, you are talking about two separate tow vehicles, that you hook the same trailer up behind. If everything is working on the trailer behind the truck, but behind the RV the trailers tail lights are inop, and the RV's tail light pin is also showing no voltage with the lights on, it's quite possibly a fuse. Look at your owners manual in the fuse section and see if there is anything remotely close to tow, tail light, or some other circuit that may relate to the towing harness. I have had a fuse go out that caused the same kind of issue. The other situation could be a bad wire. (I've had mice chew into towing pigtails and wiring before as well, or wires melt through on exhaust pipes, or that abrade on the frame.) And lastly, a wire could have come loose in the RV's connector. Colby
 
No, the rv female plug shows power to the pin 4 taillights. Just about has to be something with that actual pin. Going to take the fixture apart and look at it. It looks okay from the outside.
 
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