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What is this?

June 21, 2020, 08:57:13 am

Under the steps are my batteries.
Left one is engine battery and right one is deep cycle house battery.
Now, on the frame rail above the batteries is the "BOOST" solenoid.
On the right wall is a "doohicky" that does not show up on my wiring schematics. Does anybody know what it is and what it does? There is a red wire going to the left side of the BOOST solenoid. Why?
The blue wire comes from the BOOST switch on the dash.

Also, when I connect the red cable that comes from the left side of the BOOST solenoid to the engine battery like the schematic shows, the interior 12V system draws off the engine battery when the salesman switch is in the "OFF" position. Sucks it right down over time.

The light green wire coming from the "doohicky" and going to the ground post on the house battery sparks when I connect it. Should it?

None of this makes sense and apparently was done by other than Foretravel and no documentation.

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Re: What is this?

Reply #1 – June 21, 2020, 11:03:38 am

Just a wild-a$$ guess here...

That looks similar to some manual battery combiner solenoids I have seen for sale online.  Similar to the one in link below.

If I am correct,  I am also guessing there is a switch or circuit somewhere that activates the solenoid.

As to why it was installed...your guess good as mine.

Perhaps it automatically combines the two batteries when the ignition switch is turned to "START" position?

If it was intended to replace the OEM boost solenoid, then it should have replaced it.  IE, the old solenoid would be absent.

If it operates independently of the boost solenoid, then I would look at what the other ends of the big red cables are connected to.  If installed to connect two "things" together electrically, then knowing what those "things" are might give a clue to its purpose.

Dual Battery Isolator Relay Start on/Off 4 Pin 500A 12V for Car Power Switch...

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Re: What is this?

Reply #2 – June 21, 2020, 11:09:13 am

I recognize it as a solenoid.  Is it not the "generator starter solenoid" shown in the lower left of the schematic?

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Re: What is this?

Reply #3 – June 21, 2020, 11:30:10 am

Looking at your picture it's had to tell if the red wire from the doohicky (solenoid) goes to the left of the boost solenoid but if it
does I go with Chuck it's the isolator.

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Re: What is this?

Reply #4 – June 21, 2020, 12:08:28 pm

Thanks guys, guess I am going to have to crawl under the coach and trace the "big red wires" to both ends and then label them.

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Re: What is this?

Reply #5 – June 21, 2020, 05:35:54 pm

That relay may be a house battery disconnect relay, similar to the manual salesman switch many of us have. 

It's use is to remove power from many by not all, house loads when storing or leaving coach.

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Re: What is this?

Reply #6 – June 21, 2020, 06:13:23 pm

A green wire normally would be a ground wire, but sometimes people make repairs with what is handy, not what should be used. If you put a volt meter between that green wire and ground you may get a voltage. If so, reversing your volt meter leads will tell you if that green wire is really a positive wire (should be red) or actually is a ground wire. You may have notice that when you are reconnecting your batteries, you always connect the positive wire first, and nothing happens, but when you connect the negative you sometimes get a bit of a spark. That's because there are things that are drawing current at that instant. Perhaps that solenoid is also drawing current.

I couldn't tell for sure which is the green wire, but is it possible that the solenoid needs to be grounded and it is mounted on a non-grounded surface? I just checked my solenoids, and neither one is grounded. Both are firmly mounted on wood at the foot of the bed.

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Re: What is this?

Reply #7 – June 21, 2020, 06:18:37 pm

Just to the right of the door as you come in is the salesman disconnect switch and the cables run into the compartment in front of the door--up in the ceiling of the compartment.

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