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Old 07-10-2017, 09:13 PM   #1
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12v wiring question

I am attempting to wire a newer Atwood water heater into my motorhome. Because it is a newer model than the previous one that was in my coach, I am in need of a single 12v wire that has constant voltage to attach to the hot water tank. I have found a loom of wires near the water heater that goes to the fluorescent light above the sink. It consists of a black, white and yellow(with black stripe) wire. I know that black is positive, white is neutral and yellow is ground. Would this be a 12v circuit or not?
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Old 07-10-2017, 09:45 PM   #2
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Finding a 12 volt system to tap into is one thing ; finding one with enough available amps to power an additional load is another.
Do your wiring instructions say how many amps the new wiring will draw?
Fuse size recommendation ?
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Old 07-10-2017, 10:01 PM   #3
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Is it a 12vdc light? Likely yes. If switched at the light probably may do if the current draw is ok.
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Old 07-10-2017, 10:33 PM   #4
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Black, white, yellow.......??

Test the Voltage. Could be 120V AC for that light

Doesn't 12V DC just use POS/NEG
120V AC uses Hot/Neutral/Grd



What is model number of OLD Atwood WH?
What is model number of NEW Atwood WH?

Old one a 3E, a 8E or a 9E?
New one a 4E or 10E?

If yes..........pg 23 for wiring info
http://www.atwoodmobile.com/dealer-m...atermanual.pdf


Why aren't you using the existing 12V DC pos that went to OLD on/off switch?
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Old 07-11-2017, 10:11 AM   #5
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The old Atwood was a 3E, the new one is a 4E, so it requires 4 wires instead of 3. The 4th wire needs to be a constant 12v source. I tested the circuit to the fluorescent light with a multimeter and the voltage was 13v. Upon further research, it looks like 12v circuit voltage can vary from 12v depending on battery charge levels, etc. The wires for this circuit are flexible wires like automotive wires and not hard copper like 14-2.
Sounds like I have found a good source for the constant 12v that is needed without running a new wire the whole way from the house batteries. Thoughts?
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Old 07-11-2017, 10:32 AM   #6
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Gauge of the wire , the size of the fuse protecting it and the number of existing loads on the circuit, need to be investigated.
No sense hooking things up to existing wiring , if you start blowing fuses the first trip out.
Locate the fuse for the circuit , pull it and see what else doesn't work , with the fuse out . If it's a 20 amp lighting only circuit, with a half dozen lights, you should be fine .
What does the wiring instructions say about fuse size to protect the circuit to the W/H; that will give you a ball park figure for the power draw the new wire will put on the existing circuit.
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Old 07-11-2017, 01:20 PM   #7
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3E model had 12V DC fused source to On/Off switch....use a jumper to supply 12V DC to BOTH electric/propane on/off switches












On Edit:

I am assuming something that is probably NOT correct......you have a standard on/off switch

You probably have a 'central control/monitor panel' with the WH on/off incorporated into it by RV MFG.

So you WILL need a separate DC supply source.....

That DC to the fluorescent has the required DC Voltage BUT how MANY lights are on that same circuit >>>>>what is the amp rating of main fuse for those lights???

Water heater OEM circuit board has 2A fuse on board
Replacement boards can have 5A fuse
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Old 07-12-2017, 09:25 AM   #8
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My motorhome does have a WH tank switch built into it, so I do need the separate power source. At this point, the only thing that I can find that this 12v circuit powers is the single fluorescent light above the sink. I will take your suggestions and pull the fuse to see what else might be on this circuit. Thanks for all of the help. Will keep you updated.
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Old 07-13-2017, 03:50 PM   #9
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Traced the circuit last night. It is on a 15 amp fuse and controls the small fluorescent light above the sink, two 2" under cabinet LED lights and the toilet. I am pretty sure that this circuit should be able to carry the extra load from the water heater relay. Thoughts?
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Old 07-14-2017, 12:16 AM   #10
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Quote:
Originally Posted by Stump Jumper View Post
Traced the circuit last night. It is on a 15 amp fuse and controls the small fluorescent light above the sink, two 2" under cabinet LED lights and the toilet. I am pretty sure that this circuit should be able to carry the extra load from the water heater relay. Thoughts?
S/B good to go

Like I posted earlier......OEM Circuit Board uses 2A fuse for protection , replacement boards use 5A
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Old 07-14-2017, 09:01 PM   #11
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OK, got everything hooked up and the tank works great on both gas and electric. One final question. I am hearing a very high pitched whine coming from the circuit board area on the front of the tank. It is loud enough that you can hear it from several feet away. It makes this sound whether the tank is turned on or not. The sound stops if I pull the fuse to the 12v circuit. Any ideas on what this might be?
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Old 07-15-2017, 12:36 AM   #12
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Dirty DC..........

Using a Voltmeter set to AC
Measure the 'AC Ripple' on that DC line you tapped
Measure over 1 AC volt on the DC then that DC line is NOT going to work long term.
Will damage circuit board

Also need to recheck your wiring...........
There should be NO DC going to that circuit board UNLESS ONE of the ON/OFF switches is ON........WHITE Wire for electric and ORANGE Wire for propane
NO Other wire S/B hot unless white/orange are HOT
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