Reply
 
Thread Tools Display Modes
Old 04-19-2016, 02:33 PM   #1
Senior Member
 
Mmnsc's Avatar
 
Join Date: Sep 2012
Location: Charleston County SC
Posts: 563
Low voltage at connector for trailer lights. 5

I have a Ford F-150 with the towing package. When I hook up the trailer to the truck the running lights will not come on even though the tail lights on the truck are illuminated. The turn signal and brake lights on the trailer work fine, just not the tail lights and running lamps. I checked the voltage at the plug on the truck and it is low at 9 volts. There is continuity between the plug on the trailer and that of the truck. I am unable to get any voltage reading when I tap into the wire on the trailer side of the plug.

I have hooked up the battery directly to the pin on the trailer connector and all the trailer lights illuminate as expected, leaving me to believe the issue is with the truck and its wiring.

Since the truck shows low voltage at the trailer connector what could cause this? Could it be one of the relays or some other component. I spent a whole day trying to figure this out and cannot come up with a reasonable explanation.

Any thoughts or suggestions would be welcome.

Thanks.


Sent from my iPhone using Forest River Forums
__________________

__________________
Mmnsc is offline   Reply With Quote
Old 04-19-2016, 02:48 PM   #2
Pickin' & Campin'
 
5picker's Avatar
 
Join Date: Aug 2015
Location: South Western PA
Posts: 5,047
Most F-150's with the tow package have fuses that protect the relays that feed the 7 pin plug. Have you checked the fuses?

I'm also confused... you said you have low voltage (9v) at the plug but nothing when you probe the wire that feeds the plug. Unless something internally in the plug has melted or shorted, I don't see how that is possible??
__________________

__________________
_________________________________________
2016 Flagstaff 8529IKBS Diamond Package 5th Wheel
2017 Ford F-Series SCREW 4x4
TST Tire Monitor w/Repeater - Sinemate 3500w Gen.
Days Camped: '15=22 '16=46 '17=30
5picker is online now   Reply With Quote
Old 04-19-2016, 03:02 PM   #3
clr
Senior Member
 
Join Date: Jul 2014
Location: Sherman Illinois
Posts: 661
Sounds like you have a poor connection on that lead on your PU. I would begin by looking under the rear of your PU. On most PU's the 7 pin connector is tapped into the rear light harness. I would try unplugging the light harness under the truck and check for loose or corroded connections. While you have it unplugged check the voltage coming from the front of the truck. If your 7 pin connector has been added later and is not plugged into the factory wiring harness many times they use the pinch on type wire connectors to tie the 7 pin connector into the factory wiring. This are notorious for corroding and then making a poor connection. If they used the pinch on type connectors I would remove them one wire at a time and solder the wires together, you will never have another problem with the connection there. Hope this helps.
__________________
clr is offline   Reply With Quote
Old 04-19-2016, 03:05 PM   #4
Senior Member
 
Mmnsc's Avatar
 
Join Date: Sep 2012
Location: Charleston County SC
Posts: 563
That is what is so perplexing. I even checked the power on the wire before the connector and got the same low voltage. I also opened up the tail light and checked the voltage on the light bulb of the trucks tail light and that had the low voltage.

If I had no voltage I would suspect a blown fuse but when I checked the fuses they checked out good.

Therefore it must be something in the system that I am unaware of that is causing the low voltage on the truck's tail/running lights.


Sent from my iPhone using Forest River Forums
__________________
Mmnsc is offline   Reply With Quote
Old 04-19-2016, 03:11 PM   #5
Senior Member
 
Mmnsc's Avatar
 
Join Date: Sep 2012
Location: Charleston County SC
Posts: 563
Clr

This is a factory installed connector. That's why I checked the voltage at the truck's tail light and got the low voltage at the light itself.
Thanks for your input.



Sent from my iPhone using Forest River Forums
__________________
Mmnsc is offline   Reply With Quote
Old 04-19-2016, 03:29 PM   #6
Pickin' & Campin'
 
5picker's Avatar
 
Join Date: Aug 2015
Location: South Western PA
Posts: 5,047
Quote:
Originally Posted by Mmnsc View Post
That is what is so perplexing. I even checked the power on the wire before the connector and got the same low voltage. I also opened up the tail light and checked the voltage on the light bulb of the trucks tail light and that had the low voltage.

If I had no voltage I would suspect a blown fuse but when I checked the fuses they checked out good.

Therefore it must be something in the system that I am unaware of that is causing the low voltage on the truck's tail/running lights.
If the truck is experiencing the same low voltage problem, I would start at the main junction box that feeds the headlamp switch and trace it out.
__________________
_________________________________________
2016 Flagstaff 8529IKBS Diamond Package 5th Wheel
2017 Ford F-Series SCREW 4x4
TST Tire Monitor w/Repeater - Sinemate 3500w Gen.
Days Camped: '15=22 '16=46 '17=30
5picker is online now   Reply With Quote
Old 04-19-2016, 03:36 PM   #7
Senior Member
 
Join Date: Apr 2016
Location: Cedar Creek Lake, TX
Posts: 1,225
Ground

Be sure that you have a good ground when you check the voltage, and that the ground in the trailer connector plug is solid.
__________________
CedarCreekWoody is offline   Reply With Quote
Old 04-19-2016, 03:43 PM   #8
clr
Senior Member
 
Join Date: Jul 2014
Location: Sherman Illinois
Posts: 661
OK a factory installed 7 pin connector. But there are still plugs under the PU box at the rear of the truck that the 7 pin connector will be plugged into. I would start by unplugging that connector and testing the voltage there. It still sounds like a loose or corroded connector to me.
__________________
clr is offline   Reply With Quote
Old 04-19-2016, 05:13 PM   #9
clr
Senior Member
 
Join Date: Jul 2014
Location: Sherman Illinois
Posts: 661
Just had a thought here. Does you F150 have LED lights for tail lights? If it does that may explain the 9V measurement. That voltage is about what LED type tail lights use. But I would think that there would be a adapter/converter to allow regular tail light use on your trailer or 7 pin connector. If you have LED tail lights might be time to ask Ford about this.
__________________
clr is offline   Reply With Quote
Old 04-19-2016, 05:45 PM   #10
Site Team
 
Flybob's Avatar
 
Join Date: Oct 2014
Posts: 5,564
Many trucks have separate fuses ( and some relays) for all the trailer lights . Check manual and then check fuses and relays for the trailer running lights. They are not the same as the TV running lights.
__________________

__________________

2015 Freedom Express 248RBS
TV 2015 Silverado HD2500 Duramax
TST Tire Monitors
Honda 2000I + Companion
2 100W solar panels
Flybob is offline   Reply With Quote
Reply

Tags
light, trailer, voltage

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



» Virginia Campgrounds

Reviews provided by




ForestRiverForums.com is not in any way associated with Forest River, Inc. or its associated RV manufacturing divisions.


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 10:43 PM.