12 volt system issue

[SS Groovette]

Our 12 volt system will only operate with the engine running or when we push and hold the auxiliary start button on the dash. We have full 110 power on shore power and can invert on shore power or from the coach batteries. Just replace all the coach batteries so we know they are good. We think it may be a switch or a relay but have been able to trouble shoot the fix. Any suggestions? Heading out today and will be roughing it a bit but hope to get the fix while are out. Thanks!

[bubbles]

Engine running and aux start supplies power to the coach from chassis battery. Could your coach battery disconnect be engaged?

[SS Groovette]

No. Checked that. But thanks.

[JohnVtx]

By your batteries where all the wires connect to small terminals there may be tiny little black trip buttons. Make sure system hasn't tripped there,

[SS Groovette]

Thanks we will look at that.

[conceptumator]

In the battery compartment for the coach batteries, look on the wall for the battery isolation switch. Using a 12V tester, check both sides of it for power. Wondering if maybe whoever put the new batteries in May have turned it off. I think there is also a circuit breaker in that compartment that could have been blown during the process.


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2015 Legacy SR340 360RB with 2014 Wrangler Unlimited Toad
Gigi, Poppy and Sadie the Jack Russell (all 14 lbs of her)

[SS Groovette]

Thanks. The issue was before the new batteries.

[padcarroll]

I had a similar situation with my 2014 Legacy. I believe the dealer told me the remote switch relay was the issue. The manual switch was on but the remote switch (at the steps) was lit showing the relay was on in the battery compartment was supposed to be on but did not have 12 volt to coach. The fact that the aux start works tells me that there is a problem between the house batteries and the relay.

[Ford1]

Okay, here's my take. In close proximity to your coach batteries you have a 12VDC Power Control Box. It's usually black, about 12"x12"x8" metal and may be marked Battery Control Module. It is usually manufactured by RV Custom Products and is a Model SDC107. Looking at it from the front there should be three studs on the right hand side with large power cable coming off of each. If you have a volt meter, attach the black lead of your meter to the negative battery terminal or chassis. Then take the positive (red) lead and check for voltage on the bottom stud. This is your coach battery voltage. it should read + or minus 12 VDC. The middle stud is your chassis battery. It will probably read a little higher now since it has been charging every time you start the vehicle. The top stud is the switched 12VDC. If it does not read anything, then your Coach Battery Disconnect Relay (solenoid) is defective. If it does read 12VDC too, then you will need to make sure that the fuses inside the box are not blown, starting with F12. If you do all this and still don't have it resolved, let us know and we will try to decide the next steps.
Here is the Info on the Battery Control Box;

[SS Groovette]

Thank you both. ford1 we will look at all this. We are traveling and don't know if we have a volt meter. We will likely pick one up. I appreciate all of the suggestions.

[SS Groovette]

Thanks to everybody for their suggestions. Once we got access to a voltmeter we discovered the issue was a 150a fuse in the house battery compartment. Swapped it out and we are on our way. We did have to run around town to find one -- even freightliner didn't have one. Got an assist from Scotts Electric in Duncansville PA who called a couple of their customers for us. Now we carry a spare fuse too.

[SS Groovette]