Troubleshooting Trailer Lights

Question

Question:

so i got a 70s camper trailer and took it home. I wired in a 7 pin round plug i bought from oreillys, it had a 4 pin connector on it so i connected it, grounded the white wire on the chassis used sandpaper to insure a good connection, and then ran a 10 gauge wire to the side of the expedition to the orange and blue wire and spliced in for the black wire, tied in the blue wire to the blue wire for the e-brakes, and tied up the purple because i do not have reverse lights. After I got the harness all tied up and connected, i connected the trailer to see my progress, everything worked except the right turn signal... the brakes, and the left turn signal worked fine! so being late and happy with progress, i stopped for the night. Last night i went out and plugged it back in after work, i have zero lights! wth happened?? I pulled out the book and ran through the fuses under the right kick pannel and they all look good... used an ohms reader and tested the 4 pin and discovered that i am only getting one turn signal, the other is not working left, but works on the truck but i am fairly certain that my wiring is correct... im just lost to why i would have lights, and then all of a sudden i dont...one of the wires coming off of the truck is running 17v...thats pretty high i would think? Thats the only thing i see off... When it comes to the trailer, the battery on the trailer is sitting @ 17.5v with nothing attached. - the wiring harness for the trailer had a splice that ran to the battery and i disconnected it because it was actually killing the truck when i would plug in the trailer to the truck? but then i hooked the wires together and i had trailer lights..disconnected and they went out...idk what to do at this point but Im bummed that i just bought a trailer and i cant use it...so any advice would be amazing! and thank you in advance

asked by: Carl

1

Helpful Expert Reply:

While I'm not sure what happened, I can give you a bit of troubleshooting to attempt which hopefully helps so you can use that new trailer of yours.

You started off correctly by taking a look at the fuses and going through your owner's manual to find them, an important first step that not enough people do so we can knock that off the list. Since you said you were "fairly certain" your wiring is correct I think we should pretty much try everything just to be on the safe side. So use your circuit tester and check the wiring going into your harness from your tail lights to see if those wires are carrying the correct signals, if not then the issue is with the vehicle wiring.

If the signals going to your harness are okay, you'll need to test the signals coming out of the harness, and if they are correct then your issue is likely going to be with the trailer side wiring. I'm not sure how old the connector on your Expedition is so you will also want to check that connectors for corrosion, which can be green or white in color. A build-up of corrosion can interfere with the signals getting through the connector so if it is present you are going to need to either replace the plug or clean the corrosion.

You mentioned you used sandpaper to ensure a good ground so that likely isn't the issue but you will want to double check the rest of your wiring to to ensure there are none that are crimped, broken or otherwise damaged. I have added links to a pair of help articles on trailer wiring, including a troubleshooting guide which I highly recommend taking a look at.

expert reply by: Kyle S

1

Troubleshooting Trailer Lights

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