Trailer lights

Hi and thanks for reading.  My name is Charlie.  I recently bought a used 14 ' fun finder by shadow cruiser.  As I was towing it home I became aware that none of the exterior lites work.  Not brake lights, tail lights,  turn signals, clearance lights.  Nothing that should be operated by tow vehicle.  Any  advice?  If I should be posting this in a certain category,  please tell me which one.

Thanks,  Charlie

Welcome to the forum.

Check for a solid connection first. You probably have already done that. Then see if there is any corrosion or dirt on the male and female components. That is what happens to us most often. After that see if you have a fuse in your tow vehicle that controls your trailer connection. One of mine did, and I had to replace it. I have also had problems with a short in the wiring harness on one car. It was a shoddy job (after market addition), and I eventually needed to replace the wiring harness completely.

Note all of these problems haven't been with just one type of trailer or vehicle. We have towed cargo trailers, canoe trailers, pop ups, and travel trailers for over 35 years in vehicles from an ancient Datsun to Ram diesels. We just have had the "luck" of experiencing a wide variety of issues.

Welcome to the forum. all your trailer lights work from what ever your towing it with. start with the trailer plug, see if it needs cleaning at the spade connectors ?. do the same on your tow rig. check all your fuses. on my '00 Silverado reg cab, I have another box under the hood that holds fuses for a trailer I am pulling, there are separate fuses there for whatever I am pulling. check/clean all ground connections from tow rig to trailer. if your not getting a good clean ground ?, most lights won't work.

alan6051964 said:

... check/clean all ground connections from tow rig to trailer. if your not getting a good clean ground ?, most lights won't work....

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X2.  The fact that none of the lighting circuits work says "ground connection" to me.  Be aware that probably also means your trailer brakes aren't working.

So thanks to you guys for replying.  Now that I know I can get some good help here, I will give more info.  I sanded the connections on both the truck side and trailer side.  Then I  backed up to a flat bed trailer I also have, the lights work fine on the second trailer.  The wires on from the tow vehicle connection and the wires from the 12 volt battery system that is meant to run lights, pump, stereo on the inside of the trailer all meet in a junction box under the bench seat.  I can't tell what is what, to see if power and ground is getting that far.  Any thoughts?

Rocketcharlie said:

So thanks to you guys for replying.  Now that I know I can get some good help here, I will give more info.  I sanded the connections on both the truck side and trailer side.  Then I  backed up to a flat bed trailer I also have, the lights work fine on the second trailer.  The wires on from the tow vehicle connection and the wires from the 12 volt battery system that is meant to run lights, pump, stereo on the inside of the trailer all meet in a junction box under the bench seat.  I can't tell what is what, to see if power and ground is getting that far.  Any thoughts?

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I can't say about your junction box ?, but what I can say, is all your trailer lights should power from your tow rig. I would take a 12 volt dc test light, and start checking for power coming into this box. if it's getting to it, but not out ?, then you need to find out where/why/what is making it not send power to your lights. the inside, radio, all of your 12 volt dc lights inside have nothing to do with the trailer lights not working, as they all are on a separate wiring system. the inside works from the battery that should be on the tongue of your trailer, this battery operates all your 12 volt dc lights when not plugged into shore power. when plugged into shore power, your power converter will transform power from 120v ac to 12v dc to work all your inside lights, porch light, radio, anything that works on 12 volt dc. your fridge, hot water tank ( if electric ? ), microwave these run off of 120v ac. but to answer your question, your trailer lights, your electric brakes works from your tow rig when plugged into it .

Old Blevins said:

X2.  The fact that none of the lighting circuits work says "ground connection" to me.  Be aware that probably also means your trailer brakes aren't working.

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I agree. I chased a wiring nightmare moons ago, come to find out, the trailer tongue was not making a good ground ( old truck, new horse trailer..lol ). a bad ground will ruin your day for sure !.

OP, hook up again, run a good ground wire from your tow rig to trailer tongue/frame connected on a clean spot, see if your trailer lights work then ?. wiring for these things can be simple ?, or a nightmare !, been there, done that..lol.

Ya, the reason I brought up all the wires going into the junction box is I'm afraid if I start taking them apart to find  the power coming in, I may not get them back together right.  I'm afraid I may have to though.  I think I will try the ground wire idea posted by Alan first.  THANKS

Alan's suggestion is an excellent one.  If a good, direct ground makes your lights work, the next thing I would do is take the connector plug on the trailer apart and make sure the ground wire hasn't come loose. Good job, BTW, checking your rig on another trailer. That eliminates a lot.

Rocketcharlie said:

Ya, the reason I brought up all the wires going into the junction box is I'm afraid if I start taking them apart to find  the power coming in, I may not get them back together right.  I'm afraid I may have to though.  I think I will try the ground wire idea posted by Alan first.  THANKS

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All the wires should be color coded. Just make yourself a map as to which color on the trailer goes to which color on the cable.

Rocketcharlie said:

Ya, the reason I brought up all the wires going into the junction box is I'm afraid if I start taking them apart to find  the power coming in, I may not get them back together right.  I'm afraid I may have to though.  I think I will try the ground wire idea posted by Alan first.  THANKS

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your welcome. use a camera or smart phone ( most everyone has these now..lol ) take a lot of pics of this box before you take it apart, as you take it apart, then when it comes time to put it all back together, you can always look back through your pics, and see how it was together . I hope it's just a bad ground ?, please keep us posted .

Rene T said:

All the wires should be color coded. Just make yourself a map as to which color on the trailer goes to which color on the cable.

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agreed ^^^. if his box is anything like a junction box I found under my front floor while rebuilding it ? I think that box is like a solenoid or large fuse ?, but from what I found out, was this was just a wire junction box leading to the power box at the main breaker in the back of my trailer, and then they go to the 12 volt dc wires for the 12 volt dc lights, radio, stuff like that. his trailer lights SHOULD BE ?, on separate wires leading to all his outside lights, tail light, turn signal, clearance lights should only feed off his tow rig through his connector at his hitch. most light problems are either a blown fuse ?, or bad ground between tow rig and trailer. a 12 volt dc test light, or even a test plug they sell that you can plug right into the tow rig plug to test all power and working ground. if it's working there ?, then it's on the trailer side.

OK, so I ran a jumper cable from the tow vehicle to the trailer frame to make sure I have a ground, and still nothing.  After filing a bear spot into the metal frame, I used a test light to make sure I had a good ground connection.  Can anyone tell me where the ground wire from the plug on the tow vehicle is connected to the trailer?  In the panel at the back of the trailer?  I'm sorry for taking the easy route and asking all these questions.  I have a bad knee at the moment and crawling on my hands and knees is painful.

Charlie, a couple of thoughts:

1. I guess I'd be surprised if the problem was in the interior junction box.  Since both the exterior lights and the interior items are wired through it, if it had a bad ground, I would think your interior 12V lights wouldn't work.  It would almost have to be bad hot connections for each exterior circuit - and only those circuits.  That just seems unlikely to me.  If only one of your exterior lighting circuits was out, that junction box would be near the top of my list - but not for all three.  But I don't know how it's wired, so I guess it's possible.

2. Three things I use in trailer wiring diagnostics more than anything else are a cheap volt-ohm meter (to check for continuity), a 12V test light (the kind with a pointed probe on the end), and a light-gauge wire long enough to reach from the front of my truck to the back of my trailer, with alligator clips on the ends.

I'd connect one end of that long wire to the ground (negative) post on my truck's battery.  I'd clip the other end of the wire to the lead on the test light.  I'd make sure the trailer was plugged into the truck, then remove a readily-accessible exterior light bulb on the trailer.  Then I'd turn on the truck's lights and emergency flashers (if you're accessing a rear light).  That way you'll be sure your trying to send power to whatever socket you've removed the bulb from.  Then I'd carefully poke the end of the test light into the lead(s) at the bottom center of the socket.  If your test light comes on (or flashes because you're on a turn signal/flasher circuit), you'll know you're getting power to the socket and the problem has to be a bad ground somewhere.  The exception to this would be if you had corrosion on all your socket/bulb connections - but you can check that visually. 

If the test light does not come on, you'll know you're not getting power to the socket.

Because I'm a suspenders-and-a-belt kind of guy, If I found I wasn't getting power to the socket, I'd still want to make sure my ground was good while I was there.  So I'd use my volt-ohm meter and that long wire to make sure there was connectivity between the cylinder wall of the socket and the truck's battery ground post.

These tests will probably eliminate half of the remaining possible problems and you can focus on what's left.

Welcome to the Forum!

Rule 1.  Try the easy, simple and cheap things first!!

Rule 2 Try to eliminate causes.  Testing the other trailer eliminates the truck wiring.

Your ground check eliminates the most likely cause.

Trailer lights are virtually identical on flat bed trailers and campers.  Normally, the wiring harness is connected to ground near the front of the trailer.  Follow the wire.  The brake / turn lights are essentially a direct, uninterrupted run from the harness connector back to the rear lights.  The running lights often "daisy chain" from side markers to tail lights. 

Are you sure the wires in question actually go through the junction box?  Other wires like the power from the truck to the battery should go in there.  Brake break away wiring is probably in there, too.

With all that said, the previous owner may have done some major rewiring and run everything through this box for easy troubleshooting or similar reasons.

I completely understand the physical bit.  Can you or a teen age friend follow the wiring harness under the trailer to find  * Ground location,  * Brake wiring locations and your  * Lighting wiring?  Can they verify what wires come up to the junction box?  Do the wire colors at the harness connector match wire colors in the junction box?

Good Luck in your quest!

I had a similar problem with my tow dinghy's running lights.  The Pollak connector that was on the towed vehicle has a set of 7 pins. One is a ground pin.  I had the lights coming on intermittently, but mostly off.  The pins in this style connector are split so you can put a skinny screwdriver blade into the slit and spread the pin apart a little.  Once I did that the connector was reliable.  You might take a look to see if the pins on your trailer are also split and then try spreading the ground pin so see if that helps.

I'm getting some really good advice here.  I am going to try these ideas as soon as I get a chance, THANKS.

Since you said it was a battery on your camper that controls the lights leads me to believe you need to check for a dead cell in the battery, or corrosion.

Well Charlie, seeing how you say your lights all work on the other trailer ?, my money says its some bad wiring at that junction box. the good news is, all your lights for your running lights , tail lights, turn signals work off 12 volt dc, soooo, it's kinda hard to start a fire here !..lol. even with hooking a good battery on the tongue, won't get your outside lights to work !, this is all done by the tow truck or tow car. if you were near me, i'd be more than happy to lend a hand to help you trace down this light gremlin. if you can hook up to shore power, and your power converter is good ?, you should be able to work all the inside 12 volt lights. if not ?, then the problem is worse than you thought. try to work with one power problem at a time, start with the outside trailer lights first, all of these will work from your tow truck/car.