Battery Solenoid Switch

I have enclosed a picture of what I understand to be a battery solenoid. I thought it worked by allowing my cab battery to charge the RV battery only when the ignition key is on. But I might be misunderstanding the function and that is the purpose of my post, since the solenoid (I don't think) is operating as I thought it should. At any rate, I am not sure how to test that it is given what I have observed.

As the pictures show, there are 4 places where I have 12v at the location of the solenoid. This is true when the ignition is ON AND when the ignition is OFF. The key ignition does NOT effect the 12v in anyway.

The pole marked "Dead" is also always dead, whether or not I have the ignition ON or OFF.

It was my understanding/expectation, that when the ignition was one, the pole marked "Dead" would show 12v and the solenoid would switch to ON. However, I am not sure what test I should do to distinguish the solenoid being ON from it being OFF.

I am afraid that the pole marked "Dead" is supposed to be live when the ignition is on, and I assume that to be an INPUT of 12v, not an OUTPUT. If that is the case, then my 12v from the ignition is the problem. Perhaps my only problem. Does that mean that my "only" worry is that I am either never charging the RV battery, OR, I always have them linked such that a dead RV a battery will drain the cab battery.

Thank you for any help in understanding how this functions and how I can test it.

I also found this, already discussed on the forum:

This confirms some of my understanding, but I still need to diagnose exactly what is wrong in my vehicle.

I should emphasize that the terminal marked "Dead" is ALWAYS dead. Whether the ignition key is ON or OFF, whether the vehicle is running or not, and whether the house battery is turn ON or OFF. The terminal does have two wires attached to it. I am inclined to believe (from reading the post of the picture included) that one of the wires is from the ignition, and one is from the alternator. Though I am not sure about that. I have a hard time understanding how both could be dead if both can be independently powered. I still just don't understand enough about it.

I also do NOT have a Momentary button that I am aware of.

your picture and description is a little hard to understand, but if you have 4 different connections reading 12 volts all the time then solenoid is bad. (and it appears to be old)  Solenoids go bad.
Also not sure why there are 2 wires connected to the dead (Middle) stud on solenoid.  Is one wire a hot and other goes to ground (if so then its connected wrong and fuse is probably blown in fuse bank (40 amp fuse). 

To test old solenoid:  Unhook everything from solenoid and  take a wire suppling 12 volts to the incoming volts stud and use a test light on outgoing stud adn see if it lights up.  If it lights up then solenoid is stuck closed and bad.  If does not light up then connect a different 12 volt supply to middle stud and then see if test light lights up.  If lights up then solenoid is opening and closing like it should.

This is how I would hook up a battery isolator solenoid type switch for only charging rv battery.
First I would get new isolator solenoid. with 3 studs.  one stud for power to solenoid to close switch and one stud for incoming volts and one for outgoing volts.  To hook up, first find a wire that only supplies 12 volts when you turn key on.  this wire will connect to middle stud to supply power to close switch to allow voltage to flow to rv bats.  Next, there  should be a wire that hooks to a stud outside the fuse box and is hooked to a 40 amp fuse in fuse box (for suppling volts to charge rv bats.)  You will need to cut this wire (if not already cut) and connect the side coming from fuse to the incoming stud of solenoid and connect the side from rv to the outgoing side of solenoid.  That should do it unless there are other issues with the wiring.
       

TW, just read your second post.  There should not be 2 wires hooked to middle post.  I am guessing its hooked wrong and has blown a fuse or shorted out etc.  You need one power supply that feeds middle stud to close switch when you turn key on and to open switch when you turn key off.  You want to open switch when turning key off so rv bats dont drain vehicle bats.

Hope this all helps.  Let me know

Thanks. I doubt this will specifically help, but the dead terminal came back to life for a short period of time. So whatever my problem is, it is failing intermittently. If only one lead should attach to the center input terminal, then I wonder if the other lead is drawing power from that terminal when the ignition is on. The problem is, in that case, something should not be working but I can't find anything that doesn't work. I thought the comment in my second post implied that two leads did attach, one from the ignition, and one from the alternator. But perhaps I misunderstood.

I traced one of the center input leads (the one that goes towards the driver side). It connected to a 4-wire harness where 3 of the 4 wires wires were disconnected and capped off. One of the capped off wires was hot, but the other three, including the one that was being used, were all dead.

If my problem is tracing why the ignition wire is dead, that seems beyond hope of me figuring it out. I wouldn't know how to find the problem. I am also at a loss for what the other lead is doing. The configuration is old and has worked for years.

One more question. If one of the center leads goes to ground, then could it have ever worked? Maybe it never did (for the 3 years I've owned the MH) and I have not noticed. Maybe someone replaced a 4 terminal solenoid with a 3 terminal solenoid and connected both the 12v and the ground to the center terminal.

Is there a simple test to see if either of the center leads goes to ground?

So I have three things to figure out, why my 12v is dead, how to fix it, and what the second lead is.

Thanks. The help I already received has confirmed the basic principals for me.

well, not quite sure whats going on.  If one of the wires were connected to a ground then no it would have never worked, it would be shorting out.  Is the wire that you did not trace have power in it (did you test for power). 

I think maybe you should eliminate all of the old connections and wires and start fresh.  Identify the wire coming from the 7 pin plug that plugs to rv for charging rv bats.  Get new isolator solenoid  and hook it up correctly.  I would get a 3 connector solenoid.  There are plenty of you tube vids showing how to connect isolator solenoid.  Remember that you do not want to buy a cheap solenoid as they will get hot and prematurely burn up.  Get one that is made specific for the job.   

Specifically,  you need a CONTINUOUS DUTY solenoid, not a starter solenoid.  They may look identical on the outside, but a starter solenoid will burn out in a hurry if powered on full time.

The BOOST (not isolator and not disconnect) Solenoid is what you mention in the document

OK.
There are basically 3 types of solenoids used in RV's
Isolation
Boost and Starter
Disconnect.
Isolation is usually an energized" 100% duty cycle solenoid.  It may be activated by the Ignition or by a "Battery Control System"  if it is energized by a battery control system it may be VOLTAGE dependent. IE: pulls in at 13 volts (NOTE.. Number pulled out of thin air not out of any documentation chosen as easy to type).

The Boost (And Starter) Solenoids are operated by manual switches and/or pilot relays which are operated by manual switches.  Since operation is identical I will stick with the BOOST only. This is a limited duty (often 50% or less. hold boost button for no more than 30 seconds) solenoid  Pulls in much faster than the Isolator or disconnect also drops out faster. this is to limit arching as 100 amp loads are switched by these puppies (more or less) and the inductive KICK when the starter drops out can be real impressive!!!!!.

FInally the Disconnect... These may be 100% duty cycle like the isolator or they may ber magnatic latching..  Intelletec BCC's use the latter not sure of other makes.

THe latching work like this.. The Armature is a magnet. feed power through the coil in one way and it moves.. let's call it right. were the armature magnet locks to a metal plate.. Feed current the other way  and it moves left.  Where there is another metal plate... THe magnet "Latches" to the metal plate and the solenoid remains in that position (On or off) till you push the rocker switch the other way.  This is like a 1% duty cycle coil but a 100% solenoid. (Don't worry about that.)

All Solenoids have 4 Terminals (THE CASE MAY BE ONE OF THEM Two "Big" and two "Small" (The case is a small one)

The following applies ONLY to the small terminal(S)
100% duty solenoids (Chassis disconnect, isolator) ONE terminal (Small) will be hot when the solenoid is supposed to be engaged (ON).  Now on the ingition (Chassis battery) this will be any time the ignition is on. but on the isolator it may require engine running alternator outputting and as I said above some "Threshold" Voltage like 13.. OR some period of time (like 30 seconds) or both.

On the BOOST it will only be HOT when you push the button

And finally on the House Disconnect.. one of the small terminals will be HOT when you press USE the other when you press STORE normally both are grounded .(Chassis ground)

TW, have you figured the issue out  and fixed it yet?  Just curious 

Thanks for the extra info. No, I have not fixed yet. Yesterday I looked at it briefly. I did trace that the second input wire seems to go back to the generator. Could it work that way? That the circuit is closed if either the ignition or genset is on? I am headed to it now to test that. I have ordered a replacement cont. duty solenoid as well, and a fuse tap to run a new wire from the ignition.

Ok, just tested everything. The short of it is, yesit looks like I am just going to find a new source for 12v on ignition, and give up figuring everything else at, unless an epiphany strikes me.

1) The solenoid tested fine. It is open but closes when 12v is supplied. The 12v on the RV side that I previously measured was simply from the battery, even when the solenoid was ope.
2) The second heavy gage orange wire connected to the center terminal was not hot with the genset running, though it still looks like it goes back in that direction. I looked hard for some type of improvised Momentary switch to assist engine start from the RV battery, but none was found.
3) I also can't find were the other heavy gage orange wire was connected, or how a or what fuse might be blown. There are no taps on the fuse box. One of the two orange wires had power come back for a short time, then go dead again. I don't know which one because they were connected at the time.
4) All fuses labled for the RV battery were fine, and two fuses at the truck battery were fine.

Again, thank you everyone, and Shane (and John for info on solenoids). I'll procede with a new 12v feed unless I think of something.

One last thing, I'll also have the alternator tested. Pehaps the one of the orange wires are connected directly to the alternator and it has gone bad. I should also test to see if shore power is the second orange wire to both batteries charge during shore power.

There should be one wire hooked to the alternator (A big one at that) which may ber marked "Fuseable link" it's a fuse.

Thanks, John.