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Old 12-01-2020, 10:46 PM   #1
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Coach 12 V problem

I have been looking for a electrical drawing for the internal !@ V that is controlled by the 12 V switch by the door. My problem is occasionally at night the ceiling lights will dim and flash. the 12 v power to all items will flash or not work. This prevents the thermostat to run the heaters or AC. Sometimes I get it to recover by switching it on and off. Checked the switch and it seems ok. Is there a on off solenoid and where is it located. A wiring diagram or schematic would be very useful. Where can I get one.
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Old 12-02-2020, 01:43 PM   #2
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This sounds like classic " coach battery disconnect relay " internal contact problems .

Can't help you with location , but here's what the relay ( one of the most common) looks like . Yellow circle .
The relay is close to the battery bank usually in the next compartment to get it away from possible corrosion caused by fumes from the batteries during the charging cycle.

You can move all the heavy cables ; to one side; by-passing the relay for a test.
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Old 12-02-2020, 02:10 PM   #3
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You would get a better response if you listed the year and model of your coach.
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Old 12-02-2020, 03:25 PM   #4
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The click when you cycle the switch. Get a helper and listen for it.
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Old 12-02-2020, 04:40 PM   #5
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Found this photo of a Tiffin Red power bay , no year given , but same coach battery disconnect relay .
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Old 12-02-2020, 05:24 PM   #6
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If you can post the year of your coach it will help diagnose since there have been changes over the years. Your profile shows a 2014 38 QBA, but the photo in your Avatar is not a QBA. Tiffin does not make 38s with a tag axle.

Also, creating a signature line that shows up under each post with your RV information will let members know what you are asking about.
https://www.irv2.com/forums/f62/foru...ml#post3101035
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Old 12-03-2020, 12:44 PM   #7
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Coach 12 V problem

Quote:
Originally Posted by Lt Dan View Post
If you can post the year of your coach it will help diagnose since there have been changes over the years. Your profile shows a 2014 38 QBA, but the photo in your Avatar is not a QBA. Tiffin does not make 38s with a tag axle.

Also, creating a signature line that shows up under each post with your RV information will let members know what you are asking about.
https://www.irv2.com/forums/f62/foru...ml#post3101035
I have been traveling and have poor access to web. The photo is my previous Travel Supreme and i do not have new photos loaded into my PC.
Listed Tiffin is correct; 2014 Allegro Red 38QBA. It has a 2000 watt invertor and I don't think it has a 110 v convertor for the chassis 12 volt.
problem is during the night the 12 v drops out and causes lights to flash or not turn on. All chassis 12V items are affected and do not work properly, The thermostat drops out and no Heat or AC. Sometimes it can be corrected by switching the 12 V on off switch. No success last night with that. Chassis Batteries test ok and I talked with Tiffin and suggested maybe the 12 V switch relay going bad. I would like an accurate detailed wiring schematic or diagram of the system and a layout of where things are located.
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Old 12-03-2020, 01:21 PM   #8
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Your 2000 watt inverter , should be a combo unit ; inverter/converter/charger.

You only mention " chassis batteries test ok " has the coach battery bank tested good also?

Did you ask Tiffin about coach wiring schematics & diagrams ?

For the chassis schematics and diagrams you'd have to call the chassis manufacturer with your serial number.
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Old 12-03-2020, 04:36 PM   #9
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Quote:
Originally Posted by twinboat View Post
The click when you cycle the switch. Get a helper and listen for it.
Yes, it does not totally shut down but appears to lower the voltage so when anything is turned on it will pulse, like the lights flash.
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Old 12-03-2020, 04:41 PM   #10
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Quote:
Originally Posted by Skip426 View Post
Your 2000 watt inverter , should be a combo unit ; inverter/converter/charger.

You only mention " chassis batteries test ok " has the coach battery bank tested good also?

Did you ask Tiffin about coach wiring schematics & diagrams ?

For the chassis schematics and diagrams you'd have to call the chassis manufacturer with your serial number.
Chassis battery at 13.7 and coach battery about the same.
This has nothing to do with the chassis and I can find documentation on the freight liner end. Eventually it will just work ok until the night when you need the furnace to work.
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Old 12-03-2020, 04:56 PM   #11
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Quote:
Originally Posted by drwyatt View Post
Chassis battery at 13.7 and coach battery about the same.
This has nothing to do with the chassis and I can find documentation on the freight liner end. Eventually it will just work ok until the night when you need the furnace to work.
With the VIN or build number, Tiffin should be able to send you PDFs of schematics and diagrams for your floor plan (and *maybe* any option changes as-built).

I agree with the other replies that the likely culprit is your 12VDC 'disconnect' solenoid. The photos posted are representative. The easy way to find it is to follow the big, fat red wires from the coach battery bank positive terminal or bus bar. One of those will go to your inverter/charger and the other will go to the disconnect solenoid. Others have posted bypass information that will help you diagnose for sure.
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Old 12-03-2020, 05:16 PM   #12
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If the charger output is adequate then it does sound like the house battery disconnect relay contacts may be burned. It's also possible there is a loose connection on the relay or battery disconnect.

Do as twinboat suggested and have someone turn the disconnect switch by the door off and on while you listen for the thump of the relay. It should be located near the main house battery disconnect switch.

Your 2014 is prior to the Spyder systems so you will need a standard latching relay and there should be a part number on it. These are special relays in that the coils are not powered all the time. There is one pulse of power to close the contacts and a pulse in the other direction to disconnect. It may look like below and Tiffin's part number is 3650 but it should be available elsewhere if you can get an actual part number off yours.
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Old 12-05-2020, 05:07 PM   #13
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Decided to dig deeper and find the power switch solenoid. I found it on the back of the elect module in the front left fuse compartment.
It was failing at the time and a sharp rap with a screw driver handle made it work for a moment.
I was able to get my iPhone in and get a photo of the relay case for info.
For a temp fix I bypassed it with a large gauge wire I had.
Tried to find it on the tiffin parts site but could not. Googled the numbers in tyco relay and got a hit at Newark elect. It cost about $118 total. Leave it to some design engineer to use a $120 solenoid to replace a standard automotive one that cost under $20.00 and does the same thing and works forever.
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Old 12-05-2020, 05:21 PM   #14
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