tiredbobmarley Posted June 2, 2017 Posted June 2, 2017 Ok everyone so I need some opinions. I just replaced my trailer wiring and everything was working great for a couple weeks until now. I tested the plug coming out of my truck with a circuit tester and it all works. When I have the "not installed" wiring in the back of my truck grounded to my truck and plugged into the connection im able to get a complete circuit at the end of the wires (without the lights connected). When I connect the lights I get nothing from them. I have tested them with a battery and they do light up. Soooo....my questions..... Will the plug from my truck give a false positive if I have the alligator clip from the circuit tester attached to the truck? I didnt think so but im trying everything.... Would the trailer lights have to be mounted in order to have a ground even though the trailer wiring harness has a connecting ground coming from the plug to the trailer? Im sorry if this sounds simple. Im not well versed in electrical circuits. When I initially replaced them it was easy and worked right off the bat but this troubleshooting is driving me crazy. Thanks in advance! Quote
cfalco Posted June 2, 2017 Posted June 2, 2017 Kind of a tough question to answer the way it is asked but i think I know what you are saying. First off, the truck, if you ground your light tester with the ag clip to the truck (I always use the trailer hitch) and test the plug one thing at a time, turn signals, brakes etc, I can not see how there will be a false neg. If the light works on all those choices when testing your plug on the truck is fine. Now to the trailer, every light I have it grounded to the trailer, every one of them. Anytime I have bought new lights it comes with a very short wire (black) hanging out the back and I ground it to the mount. When you hook up your trailer to the truck (plug and hitch) the trailer ball grounds the circuit . Its that simple. Quote
Super User Ratherbfishing Posted June 2, 2017 Super User Posted June 2, 2017 Agghhhh!!!! Not trailer wiring!!!!!! I suggest you sell the truck AND the trailer and start new. Just kidding (sort of). If it was working before and now isn't, it's probably corrosion in one of the contact points preventing a solid connection. Quote
TheRodFather Posted June 2, 2017 Posted June 2, 2017 44 minutes ago, tiredbobmarley said: Ok everyone so I need some opinions. I just replaced my trailer wiring and everything was working great for a couple weeks until now. I tested the plug coming out of my truck with a circuit tester and it all works. When I have the "not installed" wiring in the back of my truck grounded to my truck and plugged into the connection im able to get a complete circuit at the end of the wires (without the lights connected). When I connect the lights I get nothing from them. I have tested them with a battery and they do light up. Soooo....my questions..... Will the plug from my truck give a false positive if I have the alligator clip from the circuit tester attached to the truck? I didnt think so but im trying everything.... Would the trailer lights have to be mounted in order to have a ground even though the trailer wiring harness has a connecting ground coming from the plug to the trailer? Im sorry if this sounds simple. Im not well versed in electrical circuits. When I initially replaced them it was easy and worked right off the bat but this troubleshooting is driving me crazy. Thanks in advance! You didn't mention if this was a 4 or 7 wire trailer plug, but either way, as far as the grounds go, yes the lights need to be mounted to the chassis of the trailer OR have pigtail mounted to the chassis, and the white wire out of the plug fastened to the trailer. You could cheat it for testing purposes by wrapping the white wire around the stud/pigtail of the light while testing each function. Agree that if it was working before but not now that you have a loose or corroded connection, if nothing works, ground connection is the common denominator and I would look there first. 1 Quote
tiredbobmarley Posted June 2, 2017 Author Posted June 2, 2017 1 hour ago, TheRodFather said: You didn't mention if this was a 4 or 7 wire trailer plug, but either way, as far as the grounds go, yes the lights need to be mounted to the chassis of the trailer OR have pigtail mounted to the chassis, and the white wire out of the plug fastened to the trailer. You could cheat it for testing purposes by wrapping the white wire around the stud/pigtail of the light while testing each function. Agree that if it was working before but not now that you have a loose or corroded connection, if nothing works, ground connection is the common denominator and I would look there first. Awesome. That may be the solution to my problems. Ill give it a go tonight after work. Thanks again! Quote
Bassin_0502 Posted June 2, 2017 Posted June 2, 2017 Had a similar problem not long ago with a new utility trailer. Drove me nuts.... Problem is almost always a poor ground. In my case, the lights needed to be mounted on an 'L' bracket which was then mounted to the trailer frame. This design requires that the 'L' bracket is grounded to the frame, which may not happen if the frame is heavily painted or if the bolts holding the bracket don't make contact. I ended up taking a 12 inch piece of trailer wire with the insulation removed and wrapped that around the bolt that anchored the L bracket to the frame. This provided a good ground and problem solved. Good luck! 1 Quote
Super User Way2slow Posted June 2, 2017 Super User Posted June 2, 2017 Before you get too wrapped around the axle about what you think is working, let me give you some suggestions on trouble shooting electrical problems. First, throw that test lite back in the tool box and get a voltmeter. Test lite will only tell you have a voltage, not how much. Second, never depend on the voltage reading you get from an open circuit, they will lie to you. Always do voltage checks with a load on the wire you are checking. A bad connection with no load can show full voltage, but as soon as you put a load on it, the voltage will drop to almost nothing. I once had a customer's equipment that was down for three days and he replace a $2,700 controller because of a blown fuse that was showing good voltage until you applied the drive load, then it dropped to almost nothing, and his maintenance guy was only checking it with no load. He was not a happy camper when I got there and in five minutes had it fixed. I told him to look on the bright side, at, least if the controller did go bad, he had a spare now. Third thing, always remember it takes to connections to make a circuit, the positive and the negative (ground, as some call it). I've seen tons of people check the voltage to something like a bulb that's not working and say it's good but never check for voltage on the negative side and continuity to battery negative. Also, remember most vehicles today use a diode interface block to connect four prong trailer wiring to the vehicles wiring. Those diode interface blocks can go bad and cause you all kinds of problems. I will also say, 80% of trailer light problems is caused by bad ground connections and people not connecting the white wire to the frame of the vehicle and the frame of the trailer. 2 Quote
david in va Posted June 2, 2017 Posted June 2, 2017 You have a bad ground! The lights do need to be mounted. As already stated. Make sure the white wire is connected to the truck chassis and the trailer frame , make sure the connection is to bare metal. 1 Quote
XpressJeff Posted June 3, 2017 Posted June 3, 2017 Ground! Ground! Might be a ground! Did you say the lights were not mounted on the trailer? 2 Quote
tiredbobmarley Posted June 12, 2017 Author Posted June 12, 2017 Thanks for all the input! You were all almost spot on. It was definitely the ground. After grounding the trailer lights and running the ground wire up to the front of the trailer it worked like a charm. Wont forget that again, haha. 1 Quote
Super User Fishing Rhino Posted June 12, 2017 Super User Posted June 12, 2017 Here's one thing to file away in your memory bank for future reference. Most vehicles have separate circuits for trailer lights and vehicle lights. Don't assume that because all the vehicle lights work that a fuse is not the problem. Been there, done that. 1 Quote
Maggiesmaster Posted June 12, 2017 Posted June 12, 2017 7 hours ago, tiredbobmarley said: Thanks for all the input! You were all almost spot on. It was definitely the ground. After grounding the trailer lights and running the ground wire up to the front of the trailer it worked like a charm. Wont forget that again, haha. Glad you found it! Bad grounds have always been my bugaboos! If you take special care to make good connections, protect the wires and have great grounds you probably won't have problems. Quote
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