Not to mention if you use a fender mounted starter relay and it shoiuld fail, a replacement can be had in just about any little town any hwere that there ia an autoparts store

matt

 

No need to apologize. I am sure there are others who will disagree with me.

I do not like isolators and do not even like to replace them. Here is why. When you install an isolator the belief is your needs are better served because you have installed something that is theory should be more reliable.

So, you are driving along and everything is working great and all of a sudden you lose battery power and pull in somewhere and the technician says, "oh yeah, you need a new battery, the one you have is dead". You get the new battery and off you go for a couple of hundred miles or less and you lose power again and you call me. I tell you to take all big leads off the isolator and tie them all together so the alternator can charge your batteries and I will fix it when you get here. Simply put, I do not like any installation that can leave a person stranded and a failed isolator can do that.

Now change over to the relay. In my experience relays virtually never failed while closed. They get carboned up inside and fail open. If I correctly understand your intentions for this installation, failing open means you can still motor down the road, you just lose the ability to charge your house battery until you get to the next town and buy a cheaper than dirt relay at any Advance Auto store or any other of your choice.

Because I spend a lot of time trying to sort through wiring diagrams dreamed up by engineers who never set foot in what I work on, I have a strong bias for simple and cheap and a disdain for all things I regard as unnecessarily complex or costly.

You are absolutely correct. A relay and an isolator both accomplish the same thing, just in different ways. Don't forget when you hook this up, you install a fuse within 18 inches of the house battery. It is code.

Good luck,

Steve

 

Hi Matt,

Totally agree!

Steve

 

Matt - I carry a spare starter solenoid in the truck, as I'm sure every Ford owner does!

Steve - Thank you for the break down. I just need something reliable and will suit my needs best. I know there are split charge relays out that, that are engineered to read on which battery (chassis or house) requires charge and will complete the charge and switch back to the other battery. Basically, I want my house battery charging while I am driving without putting my chassis battery out.

The part that confuses me on hook up is what to do with all the stuff that is wired to my starter solenoid right now ( in contact with + ), and where the alternator cable runs to, the ignition wire, the whole configuration really. I hate messing with electrical period as finding the culprit to a problem is never easy. When it comes to safety and proper installation, cost will not compromise that.

 

You know the RV industry has charged house batteries and chassis batteries together for decades with few if any problems in virtually any application you can name. All you are doing is putting a travel trailer in the bed of your truck. If you had a seven pin on the rear of your truck with a charge lead, you could use that and you would not think twice about it. You don't, so you are adding one.

I think much of the "advanced" technology I have to deal with daily is the result of engineers with way too much time on their hands and most often is of little if any benefit i.e. split charge relays. Do you know anyone who has ever had a problem with simply running a cable from the chassis battery to a relay which goes hot when the ignition is on and the relay then charges the house battery? The safety comes from the fuses you will have in the circuit. I think you are over-thinking this installation. Just my opinion and welcome anyone else to chime in.

Steve

 

Thanks for the info RV tech...but I am still at a loss on how to wire it up, I understand that having circuit fuses is crucial (before the chassis battery and before the house battery from the Isolator) Electric aspect of things make me paranoid! What I don't understand is, the isolator solenoid has 3 terminals (came with no instructions) 2 posts on either end are + "out" to the chassis and house battery. The smaller post in the middle is marked 12v which I'm assuming is the ignition trigger....question is...where does the alternator come into play? or is the house battery getting it's charge through the chassis battery and the Isolator is what opens and closes the circuit? oh my goodness.......did I just type out the answer?!....hahahahaha

 

It sounds to me like you are describing a standard relay as opposed to an isolator using diodes.

If so, the end terminals go to the batteries, one to chassis battery and one to house battery and the small center terminal is switched by a hot when the ignition is turned on. You can feed it with almost anything that is hot as it draws very little power. The body of the relay has to make good contact with the metal surface of you truck, I usually mount them on the inside of a fender as that gives you the ground.

You will have a fuse on the cable off the chassis battery and off the house battery, ideally close to the battery. That way if either cable would chafe through from either direction it is fused. I also normally use a split loom jacket to protect my cables.

This is a very basic installation so as long as you fuse it, there is no need to be afraid of it. You are also normally only charging with 30 amps as you drive down the road so you do not have to go crazy with wire size. A truck that comes set to tow will usually have a 10 ga. wire.

I think you are ready to do this

Steve

 

If I were you I'd just put a 7 pin on the back of your truck and tap into it with a standard trailer plug. Then you just unplug the camper when you don't want electrical "contamination". Plus, as someone who has a camper I can tell you no matter how big it is you always want one bigger. And odd's are someday you'll get a pull behind and then your already set up. Not to mention if you get another truck or someone wants to borrow your camper it can easily be thrown in another truck with no new wiring. IMHO it's better to do it once then to have to go back and change it again later. I have a reasonable understanding of basic 12 volt and I was confused by the relays and such.

 

That are several possibilities and this is certainly one of them. Using a relay as described in the preceding eliminates and connection between the chassis and house battery when the ignition is shut off.

Steve

 

I just make sure I unplug my truck from the camper if I'm sitting overnight for some reason like preparing for a trip. It's not really an issue for me because I usually put my tounge jack down anyway so it's easy for me to remember. I don't worry about it if I'm traveling and stop to eat or something. I also have a trickle charger on my camper to charge the batteries when it's plugged in at home or the campground so I have minimal draw while hooked up unless somethings wrong.

 

The seven pin on your truck should be hot only when the ignition is on, if it is standard OEM wiring, but there is nothing wrong with unplugging.

Steve