Does anyone know if the RV house battery isolator is integral to the truck tow electrical system on the 2001 3500 and if so where would it be located?

No isolator in the truck. You would have to buy one and install it.

I have never seen an isolator in the FSM,  .  

 Talking the charging lead maybe? I have an '01 3500, not sure what he is asking .

Anything plugged in to the trailer connector is powered directly from the engine batteries.

8 hours ago, Mopar1973Man said:

Anything plugged in to the trailer connector is powered directly from the engine batteries.

 Correct, I see what he's saying now.

 

A continuos duty mechanical relay is what I've used for many years. They work well. Mine is switched in the cab to be able to control when the camper batteries get charged. I start my truck and usually wait till the truck batteries get replenished for awhile and then hit the switch to charge the camper batteries. Usually when I get up to highway rpm I parallel in the camper batteries to be charged via the relay.

Personally I like battery isolators that use 2 heavy duty diodes and wired from the alternator to the isolator the has the main battery terminal and a house battery terminals. This way your capable of getting the most from the vehicle alternator. Diode tend to last longer because there is no contacts to burn and diodes act like one way flow valves for electricity. Where a solenoid is a switch which h now could stick closed and drain both batteries. 

I used to charge the batteries in my boat through the 7 pin RV connector. 

 

It overheated the power pin though. So I added a seperate connector.