Trailer light issues

[mtaylor17]

All lights on my equipment trailer quit working. For awhile some worked and some didn't randomly but now nothing and it has a good ground. I know it's not on my truck side. My boat trailer lights all work and so do my other trailers. Found a worn spot on the brown wire fixed it and still nothing. It has a 7 pin connector. I hooked a test light to my truck, + pos. Side & when I touched it to ea. Prong on the 7 pin it lit up for all but 3 RH stop turn, LH stop turn, & the positive prong.

Is the 7-pin plug bad?

[CatFan]

I'd be leaning toward a bad ground. It's the only thing common to all the lights. What do you mean by hooking a test light to the truck "+ pos"? Your test light should be connected to bare metal on the frame of the truck.

Hook your trailer to the truck wiring. Get a set of jumper cables and clamp one cable on bare metal under your truck and the other end of the same cable on bare metal on the frame of the trailer and see how the lights work.

[mtaylor17]

Now I could be way off ( I've never used a test light before, I watched a few YouTube videos and went to town) I hooked lead on test light to positive blade on the trucks plug and touched the light to each blade on the trailers plug. I also hooked up the truck and trailer with light unhooked then hooked the lead to the ground on the trailer and touched the test light probe to the positive blade on my trucks plug. Supposedly if you get a good steady light that tells you that you have a good ground. Is that correct or no?

[CatFan]

A test light isn't ideal for that kind of work because it can't tell you the quality of a connection. For the ground, it may be giving you good results.

Not much reason to go from positive to the lights though. The way you hooked up will give you a light if you have incandescent bulbs and the trailer wiring is shorted to the frame or connected to the bulbs. If you don't get a light, the wire could be on or open.

Check with your light from trailer ground to each of the pins with that light on to see if the signals are getting through the connectors. Be sure the connector is pushed all the way in. On my F150 with one of my trailers it takes me several tries to get the connector in all the way.

[mtaylor17]

I tried the jumper cable trick but still couldn't get any lights to come on. It could be that I wasn't getting a good ground on my truck side though. Everything on my truck is either painted or coated with that undercoating stuff. I even tried putting the cable on a couple different bolts as well

[Jonestrollingmotor]

You said equipment trailer. Is it using all 7 pins, or just 4 or 5 of the pins. The 7pin is for larger utility (which yours may be) and RVs, basically trailers with electric brakes. If you have to use a pigtail to an adapter, there could be a problem with the adapter. Does the equipment trailer work on other trucks. If yes, then there is no reason to chase gremlins on the trailer. If no, then get you a battery, set it down in front of the trailer, grab some jumper wires and start jumping. Start by grounding the trailer to the ground side the battery. Then with a positive jumper wire (I wouldn't use a test light -- they will lie to you since it takes less current to burn a test light than it does to burn a trailer light) touch the trailer brown wire (lights) trailer green wire (right turn and right brake), trailer yellow (left turn and left brake). This will give you something to trouble shoot. If all works with the test battery, then find where it grounds to the truck and make sure of good connections there.

[billnorman1]

A couple of weeks ago I borrowed an equipment trailer. It had all kinds of problems with the lights. It was a tilt trailer. I fixed a couple of bad wires and replaced one entire wire, ended up had to run a ground jumper from the tongue to the tilt frame to get the lights to work.

[mtaylor17]

Yes it has electric brakes. The 7 pin plug is wired straight to the trailer, no pig tail with adaptor. I have multiple trailers and all of them work fine with my truck. This trailer doesn't work with anyone's truck. It is a 18ft 10k flatbed trailer with no dovetail. I bought it new in may. I tried call the dealer and was told to call the manufacturer. The manufacturer wasn't any help. Their suggestion was to upgrade to led lights for a fee. I'm pretty sure if none of the lights work switching to led's won't make a difference

[Jonestrollingmotor]

Yes it has electric brakes. The 7 pin plug is wired straight to the trailer, no pig tail with adaptor. I have multiple trailers and all of them work fine with my truck. This trailer doesn't work with anyone's truck. It is a 18ft 10k flatbed trailer with no dovetail. I bought it new in may. I tried call the dealer and was told to call the manufacturer. The manufacturer wasn't any help. Their suggestion was to upgrade to led lights for a fee. I'm pretty sure if none of the lights work switching to led's won't make a difference

This tells us its a trailer problem and not a truck problem. This means to take a battery, set it down in front of the trailer, ground the trailer to the battery with a jumper cable. Use a jumper wire to probe the connections on the plug Chances are real good the trailer is not grounded properly. It should ground through the 7pin plug, but the lights will ground through the frame, so grounding the battery to the frame will be OK. If the lights work when done this way, start tracing the ground wire from the 7pin plug.

[billnorman1]

If ALL the lights don't work it certainly points to a ground situation, but not guaranteedly. John has given you a good suggestion. Since it isn't used in water, the bulbs probably haven't exploded, however it is unlikely all 4 running lights are open but it wouldn't hurt to check at least one bulb. Since you fixed a brown wire, and that's your running lights, you should check the repair. It still doesn't explain the brake lights inoperative. Put the emergency flashers on and see if they work. If they just barely glow, it's almost surely a ground issue.

[mtaylor17]

I've been crazy busy lately but I finally got around to doing some trouble shooting. Yesterday I took a battery and used jumper cab les to test the lights. On the first attempt I tried sticking the positive lead straight to the blades in the plug but nothing lit up. Then took plug apart and touched pos. Lead straight to each wire. Brown wire all lights lit up perfectly. Tried green wire then yellow wire and got nothing from either one.

[billnorman1]

The brown wire is running lights, green and yellow brake and turn signals. Be advised, the brake and turn lamps on a non-LED trailer pull a lot more current than the runniing lights, so they require a better ground. Running lights will actually ground through the bulbs of the brake lights but the brake lights won't come on. If the trailer has a swing away tongue or a tilt mechanism, run the ground connection directly to the back of the trailer. It may be, however that the bulbs are blown, not unusual if they aren't in waterproof housings.