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Re: [GMCnet] On the Road Electrical Trouble-shooting [message #334541 is a reply to message #334533] Tue, 03 July 2018 21:11 Go to previous messageGo to previous message
Rob is currently offline  Rob   United States
Messages: 651
Registered: November 2013
Location: Victoria, BC
Karma:
Senior Member
Brian:

Yes - the blue arrow is pointing at the boost solenoid.

When the boost solenoid is “turned on” - it connects the large terminals on either side together. One side is normally the chassis and the other side is the coach/house/RV. When turned on, it’s kind of like connecting booster cables from the coach to the chassis. It’s basically a starter solenoid, being used to connect two circuits together (briefly).

The dash switch that turns on the boost solenoid would normally only be used in rare (!) cases where the chassis battery is too low to start, or possibly when coach battery is too low to start the generator. When you turn on the boost switch, the boost solenoid should “click” as it connects both sides together. When turned off - it should “click” again as they are disconnected from one another.

The boost solenoid should not normally be clicking or buzzing when turning on the ignition or during starting. It wouldn’t normally be enabled during a typical start - only when you click “boost” and try to start. And it wouldn’t normally buzz - unless perhaps the voltage is so low the solenoid turns off and on as the voltage fluctuates. You can manually turn on the boost solenoid by applying 12V to it - it should “click” and connect both large terminals together.

If your connections are good (which they may not be!) - the boost switch will gang all connected batteries together to get you started. In my Royale - I have one group 27 chassis battery (front) and two coach batteries - a 24 (front) and 27 (rear). My coach batteries are switched - so in theory I could gang all three of my batteries together to get me started.

The isolator keeps also keeps the chassis and coach separate - it keeps one side from draining the other side (which could also happen if the boost solenoid was turned on when not needed), unless charging.

I can’t really tell from you picture how the green batteries are connected. I assume that you have just one chassis battery? The chassis battery should be connected to one side of the boost solenoid and one terminal of the isolator. The coach batteries will be on the other side of both the boost solenoid and the isolator.

Hope it helps - likely not!

Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath

> On Jul 3, 2018, at 5:46 PM, Brian Krikorian wrote:
>
> Hi everyone. I just drove my GMC from Seattle to LA. It was (thankfully) a rather uneventful trip mechanically, except for one hiccup. I am hoping
> I can get some 2-cent feedback here while I try to fix/diagnose the problem before the trip back. Sorry in advance for the detail.
>
> On the way down from Seattle, I stopped ¾ of the way into Oregon for a Walmart pit-stop. While I was there, I left the roof fan running (which I
> assume draws on the house batteries) but did have a couple minor chassis battery draws (the radio and compressor) that are powered on. When I got
> back after about 45 minutes, and tried to start the MH nothing happened (i.e. no turn over or sound). I had about 12.5 showing on my various voltage
> meters. I tried boost, and nothing happened. I then used my "Jump Starter" and nothing happened. Finally someone offered a jump. The voltage meter
> went to 13, and it started. I stopped for gas, and it restarted. I got to campground #1 and I plugged in (I also used a battery tender on the
> chassis battery).
>
> The next day I stopped at a rest stop outside of Redding, Ca. This time, I left the roof fan running again, but turned everything else off. Same
> thing happened and nothing worked to get it started. I tried disconnecting the wires from the battery and connect it directly to my "jump starter"
> and that didn't work. When I put the connectors back on the battery, the only eventful item was I hit the chassis and sparked the battery. I went
> back in, and lo and behold it started. I stopped for gas, and I left the motor home running. I made it to the campground in Sacramento, and shut off
> the engine. I then tried to restart, and nothing. I took the dogs for a walk, plugged in, came back 10 minutes later, it started. I also noted that
> my house batteries were drained much more than usual. I tried starting several times over the next 12 hours and it worked each time (battery tender
> hooked up).
>
> Day 3: I drove straight to LA from Sacramento. I made two short stops (rest stop and gas) and kept the engine running the whole time. I made it to
> my mom's house, and turned off the engine. This time I didn't have the roof fan running the entire time. My voltage showed 12.3-12.5. I tried to
> restart, nothing. I plugged in the battery tender, hooked it to the chassis battery......got inside and cranked it....the motorhome turned over.
>
> A few other things: In January my alternator was replaced, there were new wires put in, and a new battery. About 8 months ago I put in a new
> isolator. Finally, whenever I used to turn the key to start, I'd hear a buzzing sound for a second (which I am assuming was the boost solenoid). I
> didn't hear that buzzing over the last couple days, even when fully charged.
>
> So I'm planning to run through all the connections I can, and make sure that the connections are good and clean. The other alternative is that my
> "new" battery is not holding a charge, but that seems odd since when I hooked up the lines directly to my jump starter, it still didn't start.
> Finally, I'm wondering if the boost solenoid is bad. Although I don't know enough if that would cause this kind of problem. The good news is I'm in
> LA until next Monday, so I can hopefully make any "small fixes" while I'm here.
>
> Also, I'm assuming the item with the Blue Arrow below is the boost solenoid? I also have two other batteries (Green Arrow) that are hooked up, as
> well as two batteries next to the generator. I'm assuming the Green Arrow batteries are for extra boost?
>
> http://www.gmcmhphotos.com/photos/member-galleries/p64949-boost-solenoid-and-batteries.html
>
> Finally, if I need a new boost solenoid, does anyone have an idea of the part I order and where? I saw in earlier forum posts someone mentioned a
> Napa part, but when I checked it, it said it was a "starter solenoid".
>
> Any suggestions would be appreciated.
>
> --
> Brian K
> 1977 Eleganza II, TZE167V100261
> Bellevue, WA
> Rebuilt 455, New brake system, a lot of Original Equipment ready to fall apart (discovering more as I go along....)
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Rob - Victoria, BC - 76 Royale - Rear Twins/Dry Bath

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