bobinyelm

2003 3500

The battery charge wire on my factory OEM 7-Pin receptacle is hot all of the time.

I would have expected it to be "switched," so it's only hot when the engine is running.

Do I have a stuck relay in the OEM trailer harness system, or is the circuit "hot" on our trucks by design?

I am running a #8 wire back from the battery through a 40amp breaker, then through a 100a continuous duty solenoid to the 7-Pin and to my Lance camper receptacle, and was planning to switch the solenoid using the old (hopefully switched) charge wire, which is not switched (whether on purpose or through a fault).

If the charge wire is hot 24/7 by design, where do YOU guys tap into a "hot only when running" circuit to power YOUR isolation solenoid? If there is a stuck relay causing my charge wire to stay hot, where would it be located?

Is there an online source to show the OEM trailer harness wiring circuit?

Thanks-
Bob

torquefan

As far as I know, that circuit has always been hot on most trucks. To wire in your own circuit, you can energize the relay with any circuit that is hot in "ignition on" only. Grab a test light and check your fusebox for ignition-fed circuits.

bobinyelm

Oh.

My Ford came factory equipped w/ a relay as a part of the trailer package.

Having to unplug a trailer every time you stop to keep from draining the tow vehicle battery is a pretty crappy way for Dodge to wire it, but I guess they saved a few bucks on that plus by wiring with inferior wire gauge.

It's OK for little utility trailers, I suppose, but most truck campers or trailers/5th wheels need serious current capability, especially if running the fridge on DC.

Oh well.

FiverBob

The hot circuit to the trailer is that - - HOT - - all the time. I tow a 36' fiver with all the toys. I do NOT have a relay. I have installed them on previous trucks but not on this one. I also have a 2000w inverter in the fiver. We overnight many times on our travels and typically make some coffee, watch TV, hit the sack and maybe run the heat if necessary and do not unplug from the truck. I have never had a problem or even come close to bringing the batteries down to a critical level. I run the fridge on gas while traveling. I do have twin 6v golf cart batteries in the rig which helps I am sure, but a 2000w inverter is pretty big. I do not think Chev has a relay stock and my last Ford did not have one stock.
Bob

bigwheels94

Yeah, mine is hot all the time too. When I'm going to be hooked up for a long time in one spot, I pull the fuse under the hood to disconnect the camper from the truck. I'll probably install a relay, or switch one of these days.

tallboy

I need to run a charge line from my battery to my truck camper as well. Do you have any pics of where you tapped into your truck 12V system with your relay and solenoid? Where can I get a solenoid as well. Thanks

nwflyoda

i am not very familiar w/ this, but you can charge a battery on your trailer w/ this setup correct? i was wanting to put a winch on my trailer and have it charged by the stock charging system instead of having to run a bunch of wires to the back of the truck.

Mlucas

Chev & dodge are hot all the time, don't have personal knowledge on Ford.

My brother & I got stranded hunting this year cause of this issue-both of us ran our batteries dead - too dead to start the trucks. Need to boost to get going again.
Usually, we rely on a genny to keep it all charged....but some mice ate the control wires...

So, unless we have a genny, or only stopping for a short bit-we unplug.

Utundra

Hey Bob, On my 2005 Lance camper the charging circuit to the camper batteries is intelligent. That is to say it won't discharge the truck batteries to the point where the truck won't start.

ArkansasRam

Bobinyelm

Really hate to bust your ford bubble, but my 87 f250 and my buddies 94 f250
have the same setup as the crappy dodge you speak of.

ripping r

what a let down. i thought it was keyed since the day i bought the truck. glad it has never drained the batterys on me. i will start unpluging when camping.

bobinyelm

I don't have pictures I can post, but I simply connected to the left battery through a 40a circuit breaker($4 at any auto parts) w/ #8 stranded wire (ran the wire down the driver's side under the truck and wire-tied to various cables and lines), and put a continuous duty solenoid ($19 from any RV dealer-they are called "aux battery solenoids" and are used on motor homes*) inline I located under the bed. I activate the solenoid w/ a small driving-light relay on the firewall triggered by a terminal in the fuse box that is only hot when the ignition is on).

Bob
*http://www.neon-john.com/RV/Electric...ion_relays.htm
http://www.rockauto.com/catalog/rafr...&a=FR233-AR398
http://www.aircraftspruce.com/catalo...asterrelay.php

n2moto

Tap into your "hot" trailer battery wire to the in side of an Isolater. Put the down stream wire on the out put side. You are using the stock harness not running a bunch or wires. Then run a key hot wire to it. Check anything in your fuse box or coming out of the dash that are key hot. Install an inline fuse to that and you're gtg.

You only have to run one little wire a short distance you might get away without a fuse on it but I wouldn't.

bobinyelm

Be aware that the stock wiring harness has a single #14 wire for the trailer charge wire.

It's good for 20 amps, but will have enough voltage drop under heavy draw (say with a fridge sucking 20 amps) that the voltage to a trailer or slide-in camper won't be high enough to keep your trailer/truck-camper battery charged, especially after 25 feet of run to the bumper mounted 7-Pin receptacle, and you may find it pretty flat when you park for the night.

But if you don't care about a somewhat discharged RV battery (if you use your fridge on DC), or if you don't have any high-draw loads in your RV, then n2moto's suggestion just to splice into the factory harness wire should be fine.

If you activate your isolation solenoid using "just any" key-hot terminal in your fuse box, be aware that when the solenoid de-energizes, it produces a negative energy spike (that's how an ignition coil works, remember, when the points open, the coil magnetic field collapses, producing the spark), so I would install a shunting diode from the solenoid activation terminal to ground to keep that spike manageable just in case you tapped into a circuit w/ sensitive electronics connected to it. The diode will protect it.

I used a small relay to activate the solenoid to get around this problem, and also because since I didn't research which key-hot terminal I was using, I didn't want to load that circuit powering the solenoid coil directly (the small relay draws only 0.1 amps or less). Again, if you know the circuit you tap for activation is good for another 2 amps or so, then you can omit the small relay, and use the diode to be safe.

The Lance RV company recommends #8 wiring from the truck battery to the camper, but if #14 works for you, then no need to go to the hassles of adding a non-factory wire.

bobinyelm

I think you misinterpreted my words. If you are hurt by thinking I was saying the Dodge is crappy, then you need to disconnect your own ego from the stuff you own.

I wasn't insulting you personally by the word "crappy," I was describing the practice of cheaping out running sub-standard wiring, and then not isolating the charge circuit as my later ('99) Ford did. This is not unique to the RAM.

Chrysler has used unsafe wiring in other of their vehicles, and deserves the "CRAP" adjective in spades. In the early 2000's they actually hot-wired the blue trailer brake wire in their truck tow harnesses (part of a $250 tow package) directly to the battery circuit meaning anyone attaching a trailer with brakes couldn't even move their trailers without cutting the wire. Then, for liability reasons after the first screw-up, their engineers decided to omit the brake wire in the harness completely, with a 7-Pin receptacle that didn't even incorporate a terminal to wire to for the brake wire on later vehicles. This meant installing a new 7-Pin AND having to add a brake wiring circuit from scratch.

I like my Dodge truck, and love the Cummins engine, but when it comes to their towing harnesses, Chrysler leaves something to be desired unless one is only towing very small utility trailers. I guess when you bankrupt yourself selling cars that mostly rate "Not Acceptable" in Consumer Reports for years on end, you need to save money somewhere waiting for the taxpayers to bail you out and run you.

So far, the tow harness is my only complaint of the Ram, so no, again, I am NOT calling the truck crappy.