Rear running lights work sometimes and sometimes .... they dont?

New to fords as I have had many a dodge and Chevys.
Just picked up a new to me F250 Superduty V10 .
Everything is great except when I turn on my lights the rear tail running lights work for a bit ... then slowly (in like 5 seconds) dim out to nothing.
Brake lights , turn signals work but no running lights.
Checked the bulbs and replace all the fuses but still the same.

Ground ?
Is there a common ground for these there are mounted to the undercarriage somewhere ?
Headlight switch ?

Thx
Love my beast , BLAZAC so far though .
Cheers

 

sounds like a grounding issue

 

Trace down the brown parking light wire that goes to the rear.
You could start at the rear and move forward using a test light or a multimeter.
You will have to open the wire loom (black convoluted tubing) as you move forward
to gain access to the brown wire.

If the other lights are working the ground doesn't sound like the issue.

May be a cut in the brown parking light wire somewhere, when it starts to draw voltage
it gets hot at the cut/nicked place and the voltage drops until it makes
the lights go dim then go out.

DC (direct current) 12 volt current flows from negative to positive, not hot to ground like
most people think it does.

 

Joe's got it right. weird that it hasn't blown a fuse though.

 

Thank you.
Ill dive into it tomorrow and get back to as what I find.
Yes it is strange no fuses have blown.
They were all good in both the fuse box under the dash and in the engine compartment.
After I changed them ALL , still good but alas , fade to black tail lights lol

 

Your welcome
and to FFS.

 

Loose corroded connection at the rear electrical connector (drivers side )
Thx

 

Well I thought I had it licked!
So I found the short by grabbing the grey electrical plug behind the rear bumper driver side . When I grabbed it and twisted it , the lights worked .
Figured aha , there loose and probably dirty .
So I unplugged it and sprayed some electronics cleaner in there , let it dry and plugged it back together .
Now , the rear running lights and license plate lights dont work at all.
grabbing the connector and twisting in any fashion doesnt get them on .
What wire is the power wire back there so I can see if Im getting voltage at the harness back there ?
I still have brake and turns .
All front lights work properly .
and I have pulled every fuse in the dash box and engine bay box and there all good too.

 

FIXED!
The male portion of the brown wire in that pigtail/clip/connection had pulled 1/2 way out of the harness and was barely connecting.
Tried shoving it back thru but wasnt going to happen so I clipped both ends of of either side of the harness and butt connected them together.
Walla FIXED
thx

 

Awesome glad its fixed

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