i have a 97 f150 and about a year ago whenever i would plug a trailer into it the turn signals and brakes would work but no running lights at night, the lights that stay on all the time. i finally got around to it about a month ago and replaced the fuse under the hood and it fixed everything. yesterday it started doing the same thing again. the fuses are good and the the lights on the trailers i use are good. im lost on whats wrong now. any help would be great

 

any help please

 

possible ground in the system. do the lights flicker at all?

what are the wire colors for each circuit?

have you tested the connector right from the trailer hitch?

the goal right now, is to see if it's the truck or the trailer is the issue. if you can, can you hook the trailer up to a different truck, AND different trailer to the same truck.

you're looking for abnormalities.

ex: when i hook the truck to the trailer, the brakes work properly, but the left signal doesn't work but the right one does.....etc.

also, remove EVERY LIGHT out of the trailer, and let them hang. you're looking for corrosion, like crusty tooth paste. if you see it, clean it up and reseal it. chances are, you'll be best to cut it off and replace the wire area.

also, never use red, blue, yellow connectors. i don't trust them with my life.(bad wire connection could cause failed trailer brakes, which causes accidents on highway)

anyways.... i know i've given you lots to check over so far.

dont forget to make sure your connectiions from truck to trailer is good, as well as each connector on the trailer.

always be prepared to spend a few bucks, usually about 100. depending on the trailer.

btw, get a library card.... you'll find the chilton manuals online with this site. but we will go into that at another time. after we have tried everything else.

don't forget... i'm in your corner and don't forget to get back to me on this.

ttyl

 

You might also check the OEM connector for the plug harness. You might have to lower your spare tire to get at it (just follow the wire harness back to the OEM connector). On my 97, the plastic connector had cracked and allowed a lot of grime in, and the hitch had the ground pinched and worn down to just a couple of strands causing intermittent shorts. It was about 9 bucks to just replace the plug wiring harness.

Just a thought.

 

good point man.

all my wire work was done on semi trailers. i know semi's have a different wireing code so i didn't want to mix the op up with it.

but reading your post reminded me that usually, the semi trailers have a second plug on the rear of the trailer. even tho the 7pin has a strong spring loadded lid, id find lots of ice in winter, wet mud, etc which causes a short in the trailer, always a pita when troubleshooting issues.

OP don't forget to flex the wires to check for brittle cracked areas.

and how's it all going? been wondering how things are going with your issue

 

The running lights should be the brown wire on the truck side. You never know with trailers.

 

RV's & commercial pickups are one type. Big trucks have different wiring connections. On 7 wire RV setups, White is common ground. Black is the battery charging line. Blue is electric brakes. Green is tail, license and running lights. Red is stop and left hand turn signals, brown is stop and right turn signal. Yellow is the aux circuit.

On big trucks, white-ground, black is clearance lights and side id lights, yellow is left turn and hazzards, red is stop and antilock, green is right turn signal, brown is tail and rear markers. Blue is your aux circuit.

4 pin is super easy. White - ground, yellow is left turn and stop, green is left turn and stop and finally brown is your running lights.

Does that help you some? If you have a six pin, again it is different, but I know of few people with the 6 pin set up. Mostly 7 pin and 4 pin are the most common.

(source--Pollak wire color code chart)

 

The front lights may be on, (DRL's) but your rear lights are not on. Only when you turn on the switch should they work. Daytime running lights are only connected to the front lights. Not the rears.

 

as for semi trailers go... i was taught this way.

"the dog's tail is always brown."

meaning....

Brown: "tail" lights
red: is universtally known as stop or BRAKES.
white: is always black colored white. NEGATIVEly speaking of course.
blue: is AUX. for those thirsty days.
yellow: is LEFT because it has a letter L in it.
green: is RIGHT because it has a letter R in it.
black: is NIGHT lights. cause in the night, you'll always want them on.


so, so long as you always remember that the dog's tail is brown on a semi trailer, or semi truck... you will never forget.

 

dug into it a little deeper today, unpluged the harness by the spare tire and put a multimeter on it. the pin for running light was getting nothing to it at all, so my best guess is that there is problem at the front of the truck and not in the wires in between considered they are tapped and have conduit around it. so i tracked into the front and it joins with about fifty wires that go to the fuse box and all my fuses are good there. i didnt feel like digging into it more than that considering it could turn into a mess. so what i did was jumped a wire off my license plate lights and tied in into the brown wire which is the running lights. works like a charm now. its a jerry rig but itll work