Trailer light problem.

Subject vehicle, 99 Eddie Bauer 5 liter. Have an enclosed sled trailer. The brake, turn signals, and flashers all operate on the trailer. The running lights do not. Although the running lights operate on the Explorer. The plug is factory installed. All fuses identified for the trailer are checked and confirmed good. Testing the 4 pronged plug shows all operational except the lights. The next plug connection up the line confirms there is no power for the lights there either. All other electrical components work in the vehicle. The vehicle was never hit or damaged, all visible wiring appears undamaged. Finally, if the trailer is plugged into another vehicle, all trailer lights operate. Any ideas?

 

[BrooklynBay]

Welcome to this forum! I've moved your thread into the towing section. Take out a test light, and probe each connection on the bulkhead connector.

 

[thebrakeman]

Good analysis. You definitely have the problem isolated to the vehicle, ahead of the 4-flat connector.

When you checked at the connection "up the line" were you able to unplug that connection? Just to confirm that the problem is definitely further up the line from there?

Regarding the fuses: How did you check them? Just visually? I like to actually swap fuses (of like size). If I know the horn works, then I put the horn fuse into the problem circuit. If it still does not work, swap it back and make sure the horn still works. Also, put the questionable fuse in the horn circuit to fully test that fuse, too.

Assuming all that has been done, then you know it's between the fuse box and that up-line connector.

All I can say is keep on testing, or run a new wire.

 

[prince402]

I finally got a trailer (car dolly) to use with my 94 EX since UHaul won't rent one for the EX.

Anyway, I plugged it in today for the first time and found that I have EXACTLY the SAME PROBLEM as ScottTZ above: all trailer lights and signalling work EXCEPT the RUNNING LIGHTS, even though the running lights are working on the EX. I also have the factory installed wiring terminating in the round seven pin plug inboard of the back bumper. There is a round seven to a flat four plugged into the factory outlet. There is no running light voltage in the flat four and in the round seven factory terminal.

I haven't looked into specific fuses yet. Are there special fuses for the towing package cable?

Edit: I just checked for brake lights and they also don't work. No running and no brake lights.

 

[prince402]

Looking around this forum and elsewhere online about this problem I found that connecting into the wiring harness on the driver's side sometimes works better than on the passenger side. I also found a wealth of info at www.etrailer.com where you can drill down to your exact vehicle. For my 94 EX I found this: http://www.etrailer.com/Custom-Fit-Vehicle-Wiring/Tow-Ready/118324.html
Full, descriptive instructions are downloadable as PDF too on the linked page. The Expert Answers at the bottom are good too.
I readily found the gray connector near the jack storage place and can see that inserting the T-connector would be easy. There are also three relays fastened to the chassis there and I am wondering if they are the culprit for no Running Lights and if using the T-connector would just plain solve the problem without relay inspection.

 

[prince402]

I'm in two forum threads here on this topic trying to get all lights working. Both threads have good info.

See the other thread here: http://www.explorerforum.com/forums/showthread.php?t=244791

Very good info here including why there are multiple grounds in the Ford 7 to 4 adapter:
http://www.explorerforum.com/Singlet...lerwiring.html
More good info including battery disconnecting to reset circuits:
http://www.justanswer.com/ford/6jynz...er-wiring.html

 

[prince402]

SOLVED I now have all lights including running lights.

Before going out at it this morning I found a really good wiring diagram of the factory wiring harness in the back of my Haines manual even though there is no discussion of relays or of the harness in the text. I scanned it in high resolution and posted the link below. You can view it in your browser or right-click on it and save the jpg file to view directly in your photo editor and blow it up more if you like.

Wiring diagram scanned from Haines
http://i629.photobucket.com/albums/uu19/princeinflorida/ExplorerPostedOnline/94EX_trlr_hrnss.jpg

The next smart thing I did was to call my electronic technician friend and invite him over. He could read the diagram with much more meaning than me. Also he is very persistent and I had him read the link in one of my above replys describing the four grounds in the factory harness round 7 pin terminal. After a lot of ohming (continuity checking) he found a break in one wire leading from the relay to the round 7-pin terminal of the factory harness (in the harness after the relay). In the diagram it is the T/W wire. (Note that the colors in my 94 did not exactly match the colors in the diagram. The T/W, tan and white, in the diagram is actually B/W, black and white, in my 94 EX.) The Haines manual is for a range of years in 1st gen EX's.

So to make a quick repair, he ran a jumper wire from the running light relay output directly to the 4-pin connector brown wire at the far end of the Ford 7 to 4 adapter cable. I now have running lights and all other lights too!

Two smart things in one day is pretty good for me. Now I can take my dolly and have some non-dry-rotted tires put on it and tow my toad legally. I just don't want another Blue Light Special for lights or anything else for that matter. I hope this might help some.