dewilso Posted June 19, 2022 Report Share Posted June 19, 2022 My Daughter/SIL have a bumper pull and after they drug a bare spot in their wiring pig tail, & shorted it out I, for Father’s Day got the job to replace it. Before I did, I tried the plug in the pickup & just for drill checked for power at the pins. The Blue brake wire has power, that can’t be right….can it? I'm a motorhome person so know little of trailer operations. Quote Dave W. KE5GOH Stuck in the 70's --- In E. Texas Link to comment Share on other sites More sharing options...
Darryl&Rita Posted June 19, 2022 Report Share Posted June 19, 2022 The brakes may be getting power via the emergency break away switch. Look for a thin cable, mounted to a switch on the trailer tongue. If the pin isn't properly in place, it may be passing power. If it's missing, the switch is definitely passing power through to the rest of the circuit. Quote I have been wrong before, I'll probably be wrong again. 2000 Kenworth T 2000 w/N-14 and 10 speed Gen1 Autoshift, deck built by Star Fabrication 2006 smart fourtwo cdi cabriolet 2007 32.5' Fleetwood QuantumPlease e-mail us here. Link to comment Share on other sites More sharing options...
Kirk W Posted June 19, 2022 Report Share Posted June 19, 2022 The wire harnesses for the trailer or the tow car are exactly alike, assuming that they were wired to the standards of the industry. The blue wire is to supply power to the trailer brakes and it should not have power unless the tow vehicle brake is being applied. Even then it depends on the brake controller in use as most modern controls will lower turn off the power the trailer brake once the vehicles come to a stop. It would not typically ever reach the full 12V that is possible when sitting still. If you are looking at the blue wire and the tow vehicle is not connected, then it would only see power if the brake-away switch were to be activated. Quote Good travelin !...............KirkFull-time 11+ years...... Now seasonal travelers.Kirk & Pam's Great RV Adventure Link to comment Share on other sites More sharing options...
franco-bolli Posted June 19, 2022 Report Share Posted June 19, 2022 (edited) I had a 2004 Dodge ram and towed a really crappy rental trailer with it ONE TIME. The event shorted something in the power distribution control unit under the hood of the truck, which turned out to be a permanently mounted relay on the bottom side of the circuit board. Dodge, in their wisdom at the time, protected a 25 cent fuse with a un-replaceable relay. When the relay shorted closed, the right trailer turn/brake light was on whenever the trailer was connected. The truck turn signals worked as normal. In the OP's note, it mentioned a short and then seeing power on the blue wire. If the power on the blue wire from the truck side is on, I'd suspect a shorted relay in the truck, depending on voltage. My Tekonsha brake controller will send about 2V to the trailer brakes if I leave my foot on the brake pedal at a stop light after about 20 seconds of continuous brake application. Try disconnecting the brake controller to see if there is a change in the voltage on the blue wire. If the voltage goes away, suspect the brake controller is faulty. If there is power on the blue wire on the trailer side with it disconnected, then I agree with idea about the emergency trailer brake away pin. Electrical problems can be a real brain tweezer... Edited June 19, 2022 by franco-bolli spelling and content add. Quote +++++++++++_____________________________________+++++++++++ 2021 Ram 3500 2017 Arctic Fox 25W(to be traded??) HAM guy (Ke7FIX), photography, woodworking (mostly sawdust), Electronics Technician, USAF DAV Going where everyone has gone before Link to comment Share on other sites More sharing options...
dewilso Posted June 19, 2022 Author Report Share Posted June 19, 2022 Thanks all, what I suspected, but was looking for some validation. Quote Dave W. KE5GOH Stuck in the 70's --- In E. Texas Link to comment Share on other sites More sharing options...
Sparky242 Posted June 20, 2022 Report Share Posted June 20, 2022 If the brake controller is electronic you might read 12 volts on the truck blue wire because of leakage. When the brakes are plugged in the voltage will go to zero until the brakes are applied. Not sure if this is what's happening here but I have seen this on lots of other electronic equipment Quote 2000 Volvo VNL 610 2011 Cedar Creek 36RE Link to comment Share on other sites More sharing options...
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