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Author Topic: 7 pin trailer - running lights with no voltage  (Read 413 times)


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7 pin trailer - running lights with no voltage
« on: April 05, 2019, 01:59:02 PM »
i'm trying to use the 7 pin trailer connection on my 2017 170x sprinter Winnebago era 4x4.

i have built a wiring rig that let's me plug, just to light up a license plate frame that will mount to a cargo box.

my problem is that i'm not getting voltage to the running lights wire.  i get voltage from the constant 12 v circuit.  i have also visually confirmed that the fuse is in tact.

this video:  https://www.youtube.com/watch?v=YDh8BGD-TRQ   shows me testing these circuits with my voltmeter.  you can see that the running lights (and the left blinker) just do this weird floating 1.5 volt output thing.

what do i next debug?  why would the constant 12 v circuit be fine, but the running lights and indicators only put out a fluctuating low voltage.


Rene T

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Re: 7 pin trailer - running lights with no voltage
« Reply #1 on: April 05, 2019, 08:18:38 PM »
How old is your truck? I would disassemble the truck receptacle and check for corroded wires and loose screws. I would also check the RV plug for loose corroded connections in the junction box.
Rene, Lucille & co-pilot Buddy
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Re: 7 pin trailer - running lights with no voltage
« Reply #2 on: April 06, 2019, 09:44:25 AM »
Are you testing this with the Van running and the proper lights on?  Otherwise there isn't much voltage present when the lights are off except for the 12v power pin.   

Other possible cause is that your home made wiring rig is wired incorrectly.
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Re: 7 pin trailer - running lights with no voltage
« Reply #3 on: April 14, 2019, 11:16:28 AM »
the vehicle is a 2017. 

i have disassembled the truck receptacle and rv plug and everything looks non-corroded and tight.

i also checked continuity between all trailer circuits in the rear with the fuse box under the drivers seat.

i am testing with the vehicle running and the running lights on.  i attempted for that the be clear from the video linked in the initial post.

my home made wiring rig is fine, i know this because i've hooked it up to a known good 12 v source, and the light works great. 

so . . .

how much voltage should the running lights circuit be putting out when the vehicle is running and lights are on?   i would think this would be 12 v.  is that correct?

Ernie n Tara

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Re: 7 pin trailer - running lights with no voltage
« Reply #4 on: April 15, 2019, 11:00:42 AM »
The output of the proper pins on the 7 pin connector to ground should be +12 V. Check both to truck ground and the he tr is filer frame. Incidentally. visual checks on fuses are not always reliable.

Your symptom is a almost always a bad connection (plug improperly wired), bulb, or bad ground. Try providing a ground between the truck and trailer frames.

Ernie 'n Tara

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