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Ask Larry Welch Your Own Question
Larry Welch
Larry Welch,
Category: RV
Satisfied Customers: 84
Experience:  Master RV Tech at Hickory RV
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My 5th wheel/tow vehicle have a 7 pin plug and connector. When

Customer Question

My 5th wheel/tow vehicle have a 7 pin plug and connector. When the trailer is connected to the truck (2011 F250), only the running lights work. I checked the terminals on the truck. The power and electric brake terminals are receiving 12V, while the running lights, LH/RH turn/stop, and bake up lights are receiving <1-2V. When I activate the turn signals, the voltage goes from 0-1.3 (roughly) with the blinking of the turn signal, but the trailer lights don't reciprocate. Brake lights and reverse also do not work. I checked the relays in the power distribution box on the truck for continuity and they check out. I also checked the ground, cleaned and reattached it.
Submitted: 1 year ago.
Category: RV
Customer: replied 1 year ago.
My 5th wheel/tow vehicle have a 7 pin plug and connector. When the trailer is connected to the truck (2011 F250), only the running lights work. I checked the terminals on the truck. The power and electric brake terminals are receiving 12V, while the running lights, LH/RH turn/stop, and bake up lights are receiving <1-2V. With the turn signals activated, the voltage goes from 0-1.5V (roughly), but the trailer lights do not correspond. I checked the ground wire connected to the vehicle frame, removed, cleaned and reattached it. There was no change in the voltage. I also checked the relays in the power distribution box for continuity and they all checked out.
Expert:  Larry Welch replied 1 year ago.
Hi Larry here. This is a search and destroy mission. Please have patience. Please disconnect the RV from the tow vehicle and individually probe the 7-way on the tow vehicle with a test probe, not a continuity tester. If you have a DVM, reset it to test for 12vdc. Check the connections in each setting on the tow. Please get back to on this. Thanks
Customer: replied 1 year ago.
Hi Larry. I did that. The continuity check was only on the relays. The individual probes were 12v for the power and electric brake. All others were <2vdc.
Expert:  Larry Welch replied 1 year ago.
Okay, then on the back side of the plug you bad connections and/or a bad ground, assuming everything works correctly on the tow vehicle.
Expert:  Larry Welch replied 1 year ago.
Please get back with me, I will be off for awhile.
Customer: replied 1 year ago.
Okay I'll checkout the wires going into the plug and let you know. Thanks.
Expert:  Larry Welch replied 1 year ago.
Let me know what you find.