Breakaway battery wiring Q

[Oxjockey]

Hi all,

Just got a new (used) trailer, and the wiring is all screwy. We got the stop/turn/tail and markers working before I took delivery, now the other wiring is up to me. I've opened up the connector, and nothing goes by the standard I found.



My biggest question is the charger for the battery. It's a small Tekonsha unit, and I probed the incoming charge wire, and discovered it shorts to ground. My blue wire in the connector will also short out to ground, and I'm plainly confused. It was working for him, the battery has a charge, but I'm not sure how. I really don't want to re-wire the whole trailer...



Any ideas?





a /..... \ b

c |. . Y. . | d

e \..... / f





a Running lights - Red

b 12v+ -

c Left Blink/Stop - White

d Rt Blink/Stop - Black

e Grnd -

f Brake -

Y Yellow - unused (No reverse lights)



That leaves me with blue, which is the ground/charge wire, green, & brown.



I figured the ground and 12v+ would be easy, but no luck.







Bryan

 

[RustyJC]

Bryan,



HERE is the wiring diagram of your truck's 7-pin connector. Just wire up the trailer connector to match. You may, of course, have to chase down any trailer wiring problems such as a grounded +12V battery feed or a grounded positive feed (normally blue) to the trailer brakes.



Rusty

 

[Oxjockey]

Thanks, that would have come in handy last night! On the 2002s (at least) the wiring is molded into the cover for the outlet. I didn't discover this until later...



I guess I just wanted to confirm that I shouldn't be seeing any shorting on that wire?



Bryan

 

[RustyJC]

The battery feed wire (+12VDC) definitely should show a high resistance to ground in the trailer wiring harness. The brake wire, assuming it's a 4-brake trailer, might show only 1. 0 to 1. 5 ohms reading the trailer harness at the trailer plug since you're looking at 4 magnets in parallel. Ohm's Law says if they draw 12 amps at 12 volts, R = E/I = 12 volts/12 amps = 1. 0 ohms. This might look like a dead short to ground to a ground tester, but it's really not.



(For the electrical engineers out there, I'm using Ohms instead of Henrys for simplicity's sake since we're dealing with DC. )



Rusty

 

[Oxjockey]

So, would the 'ground' in the harness go to the brakes, and not the chassis of the trailer? I'll spend the next few minutes searching the archives.



I'm using a good HP digi tester, so I'm confident I'd see an Ohm, but I'll have to check those other free wires.



I'll look at it again tonite, crawl underneath, etc. Hopefully, I'll find something.



Thanks for your help!



Bryan

 

[RustyJC]

No, the "ground" in the truck harness must go to the "ground" in the trailer harness. The ground side of the brake magnets, -12V battery terminal, etc. should all go to the trailer chassis ground and be connected to the trailer ground wire found in the trailer harness and plug. All I was pointing out is that if you use your circuit tester to measure between the brake wire and ground, you will see a very low resistance - a "ground tester" (the battery and light bulb type) might show this as almost a dead ground.



The trailer brake positive feed wire (light blue) in the truck harness must go to the trailer brake positive wire in the trailer harness.



Rusty