I wanted to use the trailer connector on my truck to power up some 12v things I have. Not big power, just light duty.

I bought a loose connector at the auto store and wired in to the 12V (Black) and the ground (White) pins.

I measure 12v with a meter between those two... good to go.

Now I have this 12v battery charger I use for my Radio Control models. I connect it and it will not turn on. I check everything and there is 12v at the charger but it won't turn on. I connect that same charger to the battery under the hood and it works just fine. That's the way I always did it before but I thought it would be convenient to have a 12v power source at the back of the truck since we back in to our flying site. I made up this harness for a nice quick, convenient power source.

I then hooked up my cheapy 12v yellow revolving emergency light to it. It worked but it looked like it drew more current... the bulb lit for a short time brght and the motor ran faster than usual... eventually the light burnt out.

Now I'm wondering, Is this a direct 12v power source or is this a charging circuit for the trailer batteries that can't be used as a direct 12v source?

Also last season we took our camper on a three hour trip ... the batteries never charged.

Any ideas?

Thanks,

Mike

 

As far as I know, the + pin on the trailer socket is hooked directly to the vehicle's 12 volt positive, with like a 30amp limit.

I have no idea why it wouldn't run your airplane charger.

As far as trailer battery charging, there is a lot of small gauge wire between the truck's alternator and the trailer batteries. I'd expect there would be at least 1/2 a volt drop to the RV batteries if the line is carrying much current, which will greatly slow down battery charging.

 

The wire supplied by Dodge to the 12v pin is a joke. I think it's 18 gauge. I was looking at the wiring diagram for the 2004 Ram but I didn't see where the 12v comes from. Most of the circuits run through the IPM (Integrated Power Module) That thing is a bunch of relays for the trailer lighting mostly.

I suspect the current coming through that 12v pin is way to low to be of any more use than trickle charging the emergency braking battery of the trailer. I was told on another forum that that is all it is intended for. My charger is what we call a "smart" charger. It probably senses the unusable current and never turns on.

 

I tryed the same thing with my truck I made a nice harness for my cheapo 12v compressor to pump up my airbags and no go but I can measure 12v acrossed the terminals and it also doesn't charge my camper either still tryin to figure it out.

 

Don't bother trying. That 12v is only a trickle charge for the emergency trailer brake battery. I believe when you put a load on it the resistance is so great it has no current to give.

I just finished running an 8 gauge wire tonight. I put an inline 30 amp circuit breaker up close to the battery. All I have left to do is install the disconnects at the end and make up the trailer pigtail.

I talked to the RV center. They said they do the same thing. They charge $120 to do it. I didn't get specifics. I asked what size wire they use. He didn't say he just said it would be ample enough to do what I wanted. With that I decided to do it myself.

I'm using these SMH 50 AMP connectors. I picked them up at my local truck outfitter company.



http://www.parts-express.com/pe/show...number=263-110

 

hey thanks for the input I think thats goin to be my next step now

 

I just did some research in the wiring diagrams.

Looking at the pinouts at the connector (Trailer Tow Connector Add-On) Pg 8W-80-99

Cavity 4, Circuit A100 14 RD/VT Function Fused B(+)

I accounted for all other functions including Electric Brake, Cavity 7, B40, 14DG

A100 Cavity 4 is the charging circuit 12v(+).

A in A100 stands for battery feed. This is a straight run with it's only connector on the way being C217. From there it goes directly to the IPM (fuse Box) under the hood. It's connected to Fuse 19. 20 Amp. It's a 14 gauge wire.

Looking at power loss on a 14g wire supplied with 20a.... at 20+ feet you end up with 10a.

I would like to know why my circuit acts up when I put a load on it.

I hooked up a cheap revolving yellow beacon to the trailer connector. It worked but it seemed like it was getting too much voltage as it was spinning faster than normal and the bulb was super bright then burnt out. I have a feeling something is up either with the ground or the connection. It's supposed to be a straight run without any "modules" in the circuit to confuse us so it's got to be a bad wire/connection/ground. Only other thing it could be is some strange backfeeding through ground from another circuit?

Guess it really doesn't matter since I've bypassed the thing.

 

Was the truck running when you hooked up the beacon? If it's truely a 12v device and the truck was running, it was seeing about 14 volts. Not too much but enough to notice.

 

No the truck was not running. When I plugged it into the cig lighter inside it worked at it's normal speed. Makes no sense. I guess I would have to do a load test on that circuit to see how it performs but i don't know enough or have the equip.

 

Most everything you want to run on 12v can plug into a cigarette lighter plug. I like to run a dedicated switched 20A circuit to a heavy duty weather proof socket mounted in the bed - or in the trunk.

I use a good heavy duty weather proof cable, like 8g. All connections are soldered. They're weatherproofed with liquid electric tape and heavy duty shrink tubeing. Probably a lot more than is needed; but I like to over build stuff.

At the same time, it would be no problem at all to install a socket or pigtail like Hoot shows.

That will feed just about anything you want to plug in. From recharging a cell phone to powering a big converter.

 

Here's the finished product...







At the trailer

 

I like that looks very good

 

Do it once and do it right.