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Old 10-14-2009, 11:09 AM   #1
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Tracing Faulty 12v wiring

I'm sure someone out there can help solve this 12v wiring problem.

On my 2005 Fleetwood RV, I have two Dometic A&E Electric Awnings which are not drawing sufficient power - the Multi-Meter shows wires only have 3.75 VDC. To rectify- I bypassed the existing low volt 12v lines and connect to the Awning "black box" output to a reliable (lighter plug)12.95 VDC input - the Awnings all work fine. Dometic's - Diagonistic documents identify the power should be at the minimum of 12.5 VDC.

Q - What is the likely cause of the reduced power volts?

Q - How does a person back trace the wiring to find where the "lower voltage" problem is located?

Q - Does a person start from the power supply end all the way back to Dometic Black Box.

Q - How do you know which is the correct Awning wire? From the source?

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Old 10-14-2009, 11:19 AM   #2
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Definitely not an expert here, but does the voltage drop to 3.75 when you hit the "go" button or does it hang there all the time. I suspect a bad connector or the "black box" itself. Is the low voltage at the input side of the box or the output side? Bet it'll be a royal PITA to trace all the wiring. Find the fused points and check from there. There may be a relay in the circuit somewhere also with a possible bad set of contacts.

Last ditch effort would be to get a signal tracer and start at the awning end and "sniff" for the wiring at known junction points. There, that advise will cost exactly what it's worth. :-)

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Old 10-14-2009, 02:16 PM   #3
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Dometic Help

Generally Dometic can be very helpful. You might give them a call.
Bill N8HDW & Nancy N8HDV
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Old 10-14-2009, 03:46 PM   #4
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Check all positive wires for battery voltage and use a known good ground when checking voltage. Often the negative side of things are overlooked as a possible cause for voltage drops. Often in trailers, grounds or connections back through the frame are actually the real culprits. Check all grounds carefully and look for bad connections on the negative or frame ring connectors. In this case look at where the Dometic box is grounded back to 12 volts negative
Since you ran a bypass and everything works it sounds like a bad 12 volt source. Call you manufacturer and see if you can get a wiring schematic or, if none are available, track down each connection that may be feeding that + 12 volts. My guess it's being fed through a circuit breaker that's flakey. Try tracking down all your circuit 12 +DC breakers abd dissconnecting the wire from them and see if your voltage goes away at the controller. If it does thats your feed line. Then check voltage on the output of the breaker and on the input. Input should be battery voltage - a few 100ths of a volt loss through the wire. Output should be the same. if not replace the breaker. If it's low on the input side of the breaker you have a bad connection between your battery and that breaker. make sure thar breaker is wired correctly they are direction sensitive.
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Old 10-14-2009, 09:10 PM   #5
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I covered this in another post... Possible causes are:

Bad fuse, Bad connection, Nearly broken wire and my personal favorite is failed relays on the Awning control board.. Dirty contacts

That last one might be fixable if you are good with that kind of thing.. I know I'd try it,, but Ill not attempt to tell you how to do it.
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Old 10-20-2009, 12:21 AM   #6
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Harbor Freight used to sell a tool that you could trace wires with.

You hook one part to one end of the wire and the other part would pick up a signal that was generated by the first part.

Where you lost the signal was where your short was.
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Old 10-20-2009, 08:08 AM   #7
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Check the fuses.I had a fuse blow on one of my slides. I was getting a low voltage reading with my meter. When the fuse blew it coated the inside with a thin film of metal.It was enough to give a reading but not enough to run the slide.A pitted contact in a relay could do the same thing.

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