Those blasted trailer brakes

rrlund

Well-known Member
Question. Why is there a pin in the trailer plug receptacle that is hot all the time and what is the relationship to the turn signals?

I hooked on to that trailer yesterday to finish up what Royse and I started two weeks ago,that being soldering all the connections that weren't soldered from the factory. When I hooked on and checked things,I had no left turn signal. GREAT! One more thing to mess with. I had no power to the pin in the connector on the truck,so obviously a problem in the truck wiring.

I soldered all those connections,didn't seem to help much with the brakes. To heck with it,not going to mess with it anymore. I backed off the adjusters that Royse will attest to,I had tightened up so tight we could barely turn the wheels. I got the test light,turned on the left turn signal and slid under the truck. Right off the bat where the trailer wiring is spliced in to the truck wiring along the frame,I found a wire that,right next to a splice,was skinned and green. I tugged just the slightest little bit and it broke right out of the splice,lots of green corrosion fell out. I cut it back behind the connection and stuck the test light in and thought I'd get a flashing light. Nope,stayed on steady. Thing is,it's on whether the key is on or not. Just constant power to it. No flashing.

So I spliced in a new piece of wire,it started raining and just to humor myself I walked back and looked. The turn signal was working. I'd hoped for a miracle with the brakes,but not really. They will stop the truck now when it's rolling down a gradual slope. I tried it,then backed up,tried again without activating them with the lever on the controller and it rolled right past where it had stopped. Tried a couple of times. I have a little bit of drag that I can feel,but still it won't stop the wheels unless I run over a dip in the driveway. I didn't jack it back up and have anybody hit the brakes while I turned them by hand to see if I could feel an improvement that way.

A little aside,for the last year,when I hooked on and did an inspection,if the left turn signal didn't work,the brakes didn't. I found out that if I'd pour a little Coke in the trailer plug,shake it out then plug it back in,the turn signal and brakes would work. That is until recently when the brakes pretty much gave out entirely. And yes,I put a new plug on the trailer a few weeks ago when I first started messing with this thing and both turn signals worked after I put the new plug on.
 
the hot pin is on the truck ? should be for charging batteries on camper if pulling a camper

You should still be able to use the same wiring for a utility trailer that pin is omitted when the male plug is wired correctly, from trailer to truck.
 
The pin is hot in the truck,yes. I figured it might be for interior lights in a trailer or something,like a dome light in the stock trailer.

I can't figure out why the turn signal started working when I fixed that wire though? Coincidence? I moved something else and it started making contact while I was messing with it?

Doesn't make sense that it would feed to a ground somewhere does it,and complete a circuit?
 
My thoughts on why the turn signal started to work after you fixed the other wire are, Because you moved the wire around that go to that turn signal. I think all the wires in the plug need redone if you have been pouring coke in there to get them to work in the past, They are all going to need redone, Could be why the brakes don"t work also. I know that is where I would be looking.
 
rr - We've been having fits with lighting on wife's utility-cargo trailer that wife uses to haul wool products to fiberfests. Replaced plugs, wiring, etc. Seemed to work OK with my car, not hers. Crank up camper was the same way. Plug in LED tester would show good at the adapter plug (round 7 to flat 4) every time. On camper, I ran a separate ground from frame of trailer to trailer hitch mount on car. Worked some better. Was sure I had a grounding issue. Which I did... Finally took factory connector off the bracket on the car. Turns out that it is an adapter, to ANOTHER connector plug in the wiring harness. Got it apart, cleaned up the one corroded looking connector in the bunch, put some corrosion resisting grease in it and it seems to be working OK. I would sure do a real serious check of grounding. Even to running a separate frame to frame ground wire - just to ssee what happens. Good luck, neighbor.
 
Roy! that is toooo much information. Sure is a colorful sheet though. I hope rrlund is better than me at reading wiring diagrams. I am somewhere between dumber, and imbecel level. Can't spell good either.
 
Randy, I think Ray hit on it with the plug/wiring on the truck. I had to tear mine out (99 Chev), clean it all up and shined up the plug and the frame for good conenction. All the road dirt gets thrown up against there.
 
rrlund here is my phone number. Call me and I'll walk you through a diagnostic of your brake problems. You are getting mostly good advice, but if you don't follow a logical step by step process you will never isolate your problem. I will walk you through the whole thing from front to back and figure out what is wrong. It will take about 30 minutes and you will need a test light, jack, and battery or battery charger. If you use a battery charger it needs to be an older one with the analog gage and not one of the new electronic ones with a digital readout, they don't work unless they sense a battery. I have the day off and can do it today if you like. My number is 320-492-9077. If you don't want to do it today then call me most anytime. I can talk while I'm driving so unless you catch me while loading or unloading I can usually help.
 
hot wire n a 7 pin trailer hookup is for accessories or to keep the breakaway battery charged on a utility trailer.
 
If you have a truck with European lights then there is a converter under the rear bumper that converts it back to the old American system for trailers. These go bad and have to be replaced now and then.
Funny on my friends truck the hot wire go on and off with the key switch his running lights would not work from the plug on the truck so I wired them up the to the hit line. Not what we need but when in a hurry in a storm any old port will do.
Walt
 
I believe the one wire that stays hot in the plug on late model vehicles is for pulling trailers that is equipped with anti-lock brake systems. These trailers require a hot wire to feed that system at all times.
 
On trailers that have battery to apply brakes when trailer breaks away from tow vehicle, that hot lead would be used to charge the trailer"s battery. Common on horse trailers.
 
Mr. Lund

On my 2007 GMC the center pin is hot 12 volts for charging the battery for the camper .
When I bought the truck new I told the dealer that I needed it wired for pulling a camper . Guess what I didn t have a hot wire for charging the battery , so I took it back & made them fix it right.

John in AZ.
 
I believe the the reason your left turn wire was not flashing your test light is you cut it before the left tail lamp. Without a tail lamp your truck will not flash them , same as when a bulb blows. When you fixed the splice, you reconnected the tail lamp so it all would blink. That said, I still say you need a voltmeter to measure voltage under a load(amp draw)at your wheels when you apply brakes. You can hold the pedal down with a bar or stick up against the seat. As you found out, green corrosion creeps in and increases resistance and lowers conductivity of wiring. But above all else, you need to follow logical, step by step, trouble shooting, just as jon f mn says. If your brakes are working but weak, they are losing voltage or ground somewhere and a voltmeter will tell you where. You might light a test light with 6,7,8 volts but maybe you need full 12 volts to fully apply your brakes. Is there 1 or 2 wires coming out of brake ? If 1 wire it would ground thru backing plate. Your backing plate may lose ground connection thru where it bolts to axle hub. You would have to measure voltage at the plate, maybe with wheel off, to prove it out. I wish I lived closer I would love help fix this. Mark
 
Royse and I did that two weeks ago. Had some odd readings,but the same with his truck or mine. It has two wires from the brakes,all spliced in to a common wire that runs from the plug to the last brake. We had 3.7-3.8 ohms through the magnets. 12.5 volts to the pin in the truck plug and at the wire at the brakes with all the brakes unhooked from that wire down at the axles. Here's where it got interesting. I hope I remember these numbers right,but I know it dropped to 6 volts when we applied the brakes to all 4 wheels. Seems to me like we had 9 volts with 1 brake hooked up. Or maybe it was with 3 brakes hooked up. We had too many numbers flying around that day.
 
Yep, 9V across one, dropped to 6 with 3 hooked up.
Thing is, the total was 12.5V. If the brakes are dropping 6,
the other 6 is eaten up somewhere in the wiring.
Bad connection, bad/corroded wire, controller, something.
I bet it wouldn't take two hours to rewire the whole thing.
 
Gonna need a warmer day or a better soldering iron. I had a heck of a time getting things hot enough yesterday.
 
I am sure you should have more than 6 volts when all brakes are applied, but less than 12.5 v; probably 11 v or so. Your ohm reading thru the magnets sounds good. I did a quick google search and the amp draw should be 3 amps per wheel at 12v for a total of 12 amps if you have 4 brakes. Less than 3 amps per wheel you have bad connection. If your wiring ohms out good : almost 0 ohms, you may need heavier guage wire to operate the brakes, although 14ga should be good. Most meters can only take 10 amps so I would do 2 at a time or you will blow the internal fuse in the meter. I am betting on the wiring having high resistance (high ohms reading). Google search ELECTRIC TRAILER BRAKES TROUBLESHOOTING. There is a good answer under about the 4th result. Let us know Good luck, Mark
 
(quoted from post at 17:03:17 10/20/13) Gonna need a warmer day or a better soldering iron. I had a heck of a time getting things hot enough yesterday.
How tall is that trailer? Could probably back it in my barn if needed.
We'd have a windbreak, air tools and electricity. No heat tho! LOL
 
Is it possible your brake wires are hooked up in series (through first one to the second, and so on,) instead of parallel? If you have 2 wires from each brake, ONE wire from each of your brakes should be connected to the same power wire from the brake controller. ALL of these power wires should then have nearly 12 volts at the magnet with the controller fully on. The other wire from each magnet should be securely grounded, either independently near each wheel or wired together and ending up getting back through the ground circuit in your plug. If you have it wired properly and do not have close to 12 volts at all wheels, you have high resistance in the wiring somewhere.
 
(quoted from post at 22:19:40 10/20/13) Is it possible your brake wires are hooked up in series (through first one to the second, and so on,) instead of parallel? If you have 2 wires from each brake, ONE wire from each of your brakes should be connected to the same power wire from the brake controller. ALL of these power wires should then have nearly 12 volts at the magnet with the controller fully on. The other wire from each magnet should be securely grounded, either independently near each wheel or wired together and ending up getting back through the ground circuit in your plug. If you have it wired properly and do not have close to 12 volts at all wheels, you have high resistance in the wiring somewhere.
Good point Schriffs, they are wired in parallel.
Two complete wires from the front of the trailer to all brakes.
Each brake "tapped" into the two wires. Power and ground.
New ground connection at the front of the trailer frame and
a new connector on the trailer where it hooks to the truck as well.
 

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