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Old 03-01-2012, 03:34 PM   #1
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no 12 volt power without the engine running

Hey guys,
I have no 12 volt system power (overhead lights, air conditioner, etc) when the engine is not running. At first I thought it was the cranking batteries were just horribly dead so I replaced them. Next, I checked all the fuses and breakers on the panel and they are all fine. The two ac breakers on the inverter are also fine. I can get power to the GFI circuit when i am plugged into my house but nothing else. Even the generator (whose breaker is on and working) will not power anything unless the engine is running. The 12 volt switch will turn everything on and off while the engine is running, but won't do anything unless its running. I have a 1999 Airstream Cutter bus. It has a Freightliner chassis. Does this sound like a simple fix somewhere? I don't know even what to check next. It started doing this during the winter when I killed the cranking batteries trying to start it. I was using the slave switch when the genny was running to try to get some power to the cranking batteries. I just figured that I killed them so bad that the entire 12 volt system would be down until I replaced them.....help.....please.....

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Old 03-01-2012, 04:52 PM   #2
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Well the first things to check are both the positive and negative nbattery cables. Go to AutoZone or some parts place and get a special battery brush and cleam inside the cable connectors and battery terminals. Then check the negative cable where it is attached to the frame and make sure it is clean and tight. I would recommend also buying a 12 v test light and use that to see if it lights on the positive battery cable then check both posts on the 12 v battery disconnect switch and keep folling that 12 volt cable. The other possibility is the "salesman" switch is off or the relay it controls is bad. Check those circuit breakers on that inverter/charger again and make sure they are reset correctly. Then check yout inverter control panel and make sure it is actual on. Use that 12 v test lamp and see if you in fact have 12 volts going into the inverter on the big cable. Let us know what you find to that point and we can go from there.

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Old 03-01-2012, 05:24 PM   #3
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no 12v w/o engine running

you said you replaced the starting batterys? have you checked the house batterys? sounds to me like the house batterys may be dead and when you run the engine you get 12v from engine altanator lee
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Old 03-01-2012, 05:48 PM   #4
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Here is some reading of your power systems in your coach.
Your house batteries are going to supply the 12 volts for most of your controls for fridge, 12v lights, furnace, water heater etc,etc.
The battery cut off switch has to be operated for these control boards to get the 12 volts.
98KSCA, 99MACA, 03 KSCA-3740- 8.1 Chev-- ALLISON Trans, now in good hands
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Old 03-01-2012, 06:04 PM   #5
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Is your battery boost switch a three position rocker switch? You called it a slave switch. If you used it to start your engine make sure it is in correct position. Mine kills the coach batteries/power in the up positon. If it is correct you may have a bad solenoid in the main DC load center. If you don't know where it is you can listen for solenoid click when you push the battery boost/emergency start button.
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Old 03-01-2012, 07:16 PM   #6
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I had that problem a couple of years ago. I'll cut it to the quick. Had new batteries put in(mine were swelling up), and it was ok. When I got home, it happened again. My guy said bring it right back. Two of them checked everything from the battery to the solonoid. It seemed when he pressed the tester against the solonoid connection, he was pressing against a loose connection, making it ok. Anyway that was the problem. Tightened the connection and everything has been ok since.
Hope this helps
Joe from Ct.
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Old 03-02-2012, 04:59 AM   #7
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I checked the house batteries when I originally discovered the problem and they were all good. However, when I went to check them yesterday I found that one of the terminals on one of the batteries literally melted off the top. I guess it was on good enough for me not to notice the first time. I was cleaning all the terminals this time and the screw on terminal just fell off....
Anyway, I hope I found the problem. Now I wonder if a battery shop can just replace the terminal or I guess I will buy another. Too bad, the battery still reads 13.4 volts. I will repost later and tell if that was it.
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Old 03-02-2012, 04:19 PM   #8
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Ok, it was the battery. Got good power now. It was just loose enough after it melted to not have a good contact. When I tested it with the meter it was still reading 13.4 volts. Oh well, thanks for all your help with the replies! Now to fix the roof leak.....

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