My 2000 Excursion 7.3L PSD has the factory round RV style trailer plug. I have electric brakes and the left side stop/turn working.

The marker lights and the right stop/turn is not getting power.

I pulled the extension harness from the back side of the plug, thinking the most obvious was that the plug was no longer serviceable. I did start by using a multimeter to check for 12V signal at the plug. There is no 12V signal for the marker or right side stop/turn at the plug. Anyways, that is why I pulled the extension harness from the back of the plug to then try to verify I have 12V source at the end of the extension harness. I do not.

Next, I went up to the main harness on the frame beside the fuel tank and pulled the extension harness plug out of the main harness. My thinking was that the extension harness must obviously have broken wires, so I will hit the main harness plug that the 18" extension plugs into with the multimeter and verify my 12V signals there. Same thing, I get the left side stop/turn and I get the 12V brake signal, also we have ground at all connections... but no marker and no right side stop/turn power.

So, some questions come to mind. Note that the Excursion has all lights functioning fine.

I had originally assumed that the trailer lighting would just branch off of the main harness that supplies to the excursion tail lights. I concluded that this can not be, as the Excursion lighting is all good and yet trailer lighting is not. There must be a dedicated straight shot for the trailer that stands alone from the truck light system?

Another thought is about the electronic brake control, do the lights route through the electronic brake control, and can it be partially bad and causing some lighting to get to the trailer and some other lighting to be open within the brake control?

Any ideas? I'm a week away from hauling 7 motorcycles across the country on my 28" flatbed and running out of time and ideas!

Can there be a fuse some place that could kill off part of the trailer light system?

The Excursion has 86K miles on it and is garaged, it is not a rotted out or beat up old truck... Never crashed... so I doubt I have pinched or mechanically destroyed wiring. Who knows?

Any sage advice is appreciated!

 

There are separate fuses that control the trailer lights. They are under the hood.

 

fordtrkpuller,
I have the 2002 wiring diagrams so hopefully they are close to the same as your truck.

All these components are in the central junction box (CJB).

Fuse F2.6 supplies power to both the left and right turn signals thru K353 (left turn relay) and K352 (right turn relay), then the signals go thru various connectors to the trailer connector.

The running lamps are supplied by F2.38 and K356 (parking lamp relay).

I would first reseat/swap the relays involved. This may be your only problem.

Good luck.

 

Thank you. When I go home I will test these.

So it is true that the trailer lighting is a dedicated path and not simply a tie into the 12V being sent to the tail lights. I would have not suspected that, but it appears I thought wrong!

Thank you again!

 

fordtrkpuller,

True, according to the schematics. The relays are dedicated to the trailer connector circuit.

For future reference, K355 is for the charging contact and K357 is for the reverse lights contact in the trailer connector.

 

Could one of these relays be it? This is a photo of the driver's side fender. Top there is the brake booster.

 

Any chance you can use your manual and take me a couple photos of the locations of these relays? Or.. are they all labeled with the designations that you provided?

 

I would check all your fuses up front. When you play with the trailer wiring it is easy to short them out one at a time.

 

SOLVED.

There is a large "Battery Junction Box" on the drivers inner fender, behind the air filter housing. There were 3 blown 7.5 amp fuses in there. I did not know that box existed, I was looking at the under dash fuse panel not realizing that I was only seeing about half of the fuses.

 

yeah, I went through the same thing first time I went to hook up a trailer.........

 

There are 2 fuse boxes and the one under the hood controls most of the trailer wiring. You need to monitor them as you are fiddling with the wires in the back or you will be hooking up dead wires. It takes 2 people and a little probe type tester

 

Sorry if I caused you any confusion.

There are fuses and relays both interior and under the hood.

I assumed you were familiar with both.

Good luck with your trip and be safe.

 

Hi guys, I have a 2001 excursion limited.
I have 2 issues:
1. no power to the trailer fuses in the fuse box located under the hood.
2. No power to side mirrors. The turn signals on the mirrors don’t even work. I checked the fuse in the cab under the drivers side and that’s fine. Cab lights and power seats work fine. So frustrating...

 

How bit is this "Battery junction box"? I have same issue.