I was reading a couple of different threads and have a question on the 12 volt hot to the trailer--(this is my first diesel/first Dodge/first cummins) the 12 vdc positive is hot all the time on this truck. I'm use to the vehicle/engine battery being isolated from the house/trailer battery. 67 Olds delta 88 custom (425 ci engine) and an E150 Ford (300 ci inline 6) as well as the 88 E350 ford (460ci FI) all allowed the isolation device to be placed in the charging circuit from the altenator to engine battery. The device decided which battery to charge based on the voltage of the batteries. The posts were marked as the engine got first preference for charging and serving the electrical load with the second battery getting the "left over" as available to keep the house battery charged while engine was running. When the engine was off (alternator not producing) the 12vdc positive was 0 volts. Having read the threads about stopping/camping and running items on board I realized my situation of not being isolated. Soooooo how hard is it to get a battery isolator into the 03 tow package since the 12vdc positive comes out of the fuse panel on the truck? Does anybody out there have one on board?

 

I'm not sure I understand the question. With my 5er, I simply don't plug in the 7-pin connector until I've started the truck,and unhook before I camp. My 5er has a charge circuit in the 12V power supply when 120VAC is available. If dry camping, hook up the truck while idling and recharge if necessary.

I wouldn't worry about the camper battery pulling down the truck batteries if the engine is running.

I've hooked to a discharged trailer battery and have had no ill effects. I think the isolator is more for folks that may forget to disconnect their trailer. The isolator ahs some volotage drop associated with it that might reduce the ultimate charge to the trailer batery.

 

John_C appreciate the assurance on the truck batteries. "Dually" has dual batteries which I never had before (another first for me) so I guess - not to worry - is the key phrase. Yes I always have the engine running when I hook up and will learn to disconnect when parked. Simple enough step. Had the same response at work from a gasser pulling a Holiday Rambler for many years. Thanks!

 

I use to put isolators in all my TV but back in the 90s the tow package was a fuse so just unplug if not running for a long time. The old iisolators let the TV charge both batts but each batt could not be discharged from the other.

 

I'm not sure I understand the issue either, but it sounds like you're of the understanding the +12VDC at the 7pin connector goes to the batts inside the camper? It does not.
That +12VDC at the hitch is designed to keep a small 12v rechargeable drycell break-away battery (mounted on the tongue of new trailers) charged. That break-away batterys only purpose in life is to engage the electric brakes when the trailer comes off the hitch, hopefully while the safety chains remain attached.
There is a +12VDC lug that connects directly to the battery (before the fuse relay panel) that allows custom cable connections, you just have to open the lid that covers it and run a new fused circuit.
Nat

 

not!
Only some of the new trailer charge the..GEL-CELL(not dry cell)breakaway batteries if you don't have one you have to charge it yourself. My goosneck uses the truck battery to run all the loading lights ect,and it charges the breakaway battery(new trailer) If I leave the lights on lookout dead truck battery. I think if I understand what you need is a Battery Isolator (DIODE)between the truck system and the trailer system...it will prevent the trailer from running the truck battery down but still charge the trailer battery when the truck is running. It can be mounted in the 12v power sorce line anywhere in the 12v supply in the trailer itself.

 

xyzer-I think your closer to what I was thinking than natstayl. He really got me confused!! "Dually" has a 40 amp fuse in the electric box under the hood, so I know they expect to put a HEALTHY charge back to the trailer. You mentioned all the loading lights so I think your closer to my idea that there is a current flow of some size on that 12vdc positive pin. There are two deep cycle batteries on the trailer. While driving there is an inverter that does 12vdc to 120ac to run the trailer refrig (gotta keep the butter hard). I saw a disaster as a kid from a LP gas leak on a trailer going down route 9. Left a very lasting impression!!! not to say anything of the nightmares! So we do not use gas refrig in transit.
Any idea of diode size? I suppose radioshack might-They say you have the ? we have the answer! Thanks for the idea/info.

 

I'm not sure but it would have to handle 40 amps anyway and maybe a 30 amp fuse between it and the battery to keep you out of trouble. I did a search on google and there were some options or maybe go to an RV place and see what they have to offer. How much does the refer draw.....I bet a few amps....my search hit on alot of marine applications. But the RV guys have the same problem. I see they even use a selinoid placed in the 12v supply line that is wired to the key. it activates the line when the key is on...breaks the supply when the key is off. The battery isolaters tend to come off the alternater and are rated at 70-120 (and bigger)amps! but you would have abandon the current 12v supply line and run a heavy wire to handle alot of amps. I guess the answer depends how many amps you need to operate the trailer system while driving. I will probably go with a selinoid($17.00). I will put a battery in the trailer for lights and use an ice chest. It will charge the battery but if i forget to shut them off the truck won't be affected.