i posted this in trailer section as well

this week i have been chasing a weird NO trailer and then connected , then not connected on the highway it stays "connected" but once on surface streets and unsmooth roads causes the unconnected messages
this trailer towed for years behind the 2016 expedition, zero issue and towed behind my 40 foot motorhome since 2009 with no light issues

i spent the morning a most of afternoon, replacing ALL the wiring. new pigtial with 7 pin connector, new break out box, new wiring to the led tail lights and marker lights, all with a dedicated ground at each light, that is also tied back to the ground wire in the harness loom, up to the ground on the trailer frame that is fresh and is making contact according to the OHM meter

i first tested entire system with a 12 v battery on each circuit as i moved fwd from rear lights to front of trailer. everything worked.
then i tested all circuits inside the break out box before i connected the pig tail that plugs into truck
everything worked.

then i plugged pig tail into truck with it running and verified each wires position and function, (stop< turns etc.) had 12 volts on running lights and 12 then down to 4 on turn signals then it went back to 12v
had 12v on black wire and everything worked 100 % on pigtail. then i attached the pig tail to the correct circuits in break out box and then tested it all with a battery applying voltage to the lights. 100% worked.

then i plugged in pigtail to truck
lights worked, turns signals worked, brakes worked and had 12 power for accessories. then truck gave me message trailer was disconnected, then connected, then dsiconnected

so i opened up break out box and tested for 12 volts on running lights, i had 12 volts on pig tail side, it would start at 12 on trailer side then drop to 4 then back up to 6 volts.
turn signals did same thing, 12 ton 4 then 0 then no more than 6 volts...truck again said no trailer found, if i manually actuated the trailer brakes the message would say trailer connected

so i unplugged truck and crawled under and opened up the connectors on the trailer tow plug and made sure no corrosion or dirt. i had cleaned these a few days back as well, but wanted to double check.

plugged truck back into trailer and it worked for a few minutes then started the no trailer bit

i then noticed a few leds not working on the taillights...so i have dispatched a person to the trailer parts store to get two new lights )led)
i am wondering if the low current draw on the leds to cause the truck to "not see" the trailer?

 

Read this thread, may help you
https://www.ford-trucks.com/forums/1...essages-4.html

 

Yup I saw that as well.
I get full.ppwer if I disconnect pigtail trailer connector from break out box.
this trailer was towed several times throug several milesof mud and water up to axles at deer lease, never an issue.
but today. I found lots of iffy wiring so all got replaced. New lights just arrived . So tomorrow I will see if tgey mske a difference

 

update
replaced the rear light with NEW exact replacements, as in same freakign brand and lights (hopkins LED)
double checked all grounds
used a 12 volt stand alone battery and checked ALL the lights and functions with battery at the junction box, with pig tail disconnected and every thing worked perfect. then i tested the whole trailer again with pig tail connected and using the end of the 7 pin pig tail . everything worked perfectly


then i hooked truck up, with it running and no trailer detected, then detected..cycled the trailer brake a few times and truck saw trailer, i turned on four way flashers and the rear lights flash but about half the light intensity as with straight 12 v battery
then i tested running lights and they worked...well sort of . the side marker lights full bright but the tail lights NOPE not even dim,
but they all work with a 12 v battery.
so i disconnected the pigtail at the junction box and test voltages from truck through the pig tail
lights 14 v, disconnected and then drops to 4 volts if i reconnect the trailer running lights back in to the pig tail at the junction box.
retested ground between truck and pig tail and it had continuity according to the OHM meter.


so next i am placing a 4 flat connect and see if it works using my wifes edge.
a note
i also removed and re-inserted all trailer tow fuses to ensure they were not failed and seated well

 

Had a Bargman 7-pin connector I used when towing a 24ft box car trailer with my old '87 F350. Found I had to use a bungee cord to keep the connector well-seated into the truck's receptacle. If I didn't, the plug would not constantly maintain a good connection. I'm not saying that's your problem, but just throwing it out there for consideration.

On a different note, I found the factory service manual for my '05 Excursion provided the wrong wiring diagram for the 7-pin receptacle ... had a couple wires reversed when compared to the industry standard wiring diagrams. But the receptacle was wired correctly even though it did not agree with the Helm factory service manual.

 

FIXED FIXED
i put in a flat four pigtial into the junction box and hooked up my wifes edge. BOOMMM all the lights worked perfectly, and bright
so i connected same flat four to the truck and BOOM all lights worked perfect

so i sat there staring at the two pig tails and thought the only difference is the brake controller hookup in the 7 pin and no brake in the flat four
so i disconnected the breakaways switch which ixs new as well and and connected brake feed directly to the 7 pin ..boom every thing worked perfect, i even jiggled the connection and it stayed connected on dash
so i opened up the break away battery box and the battery is .08 volts, yep .08 . i will try to charge it and then connect the battery feed from 7 pin to the positive side and see if it will charge battery.
funny thing is the original 7 pin and harness i just replaced only had five wires in and was not connected to the battery.
so since 2009 it has just been a paper weight

if battery fails to charge i will steal one from my deer feeder

and yes the hopkin pre wired pigtail is not wired the same as the truck. i had to wore check each feed to make sure it was correct. power, brake and ground were correct color and position, but the running lights and signals were off color but right position

 

got a new break away battery and then replaced all of its wiring to the junction box, re-connected break away switch and a charge line to break away battery
all is good again.

weird how truck could sense the draw of a dead break away battery but not give some indication as the problem.
now i have all new from bow to stern so we should be good for another 5 or so years

 

Yeah, it's strange that these trucks can sense a bulb being burnt out, and often identify which bulb, but can't identify a dead break-away battery.
Glad to hear ya' got it all sorted out, and rejuvenated all the wiring, too! You should be good to go for awhile.