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Old 05-08-2011, 04:53 PM   #1
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12V DC Light Help needed

Anyone,

All my 12 V interior lights were working. While removing the bath fan to repair leak around vent on roof, I accidently touched the two leads to the fan motor. This blew a 30 amp fuse located in the Univolt. Ya, I should have disconnected power, I knew this but won't forget the next time! I replaced the fuse, it did not blow but I still do not have bath or rear end DC lights. No other fuses are blown, I checked for power across the one that was blown with a new fuse and there is power there. Is there another fuse panel besides the one in the Univolt? Or any other advice?
I just started working on this 79 Argo a week ago, its not in too bad a shape, just needs a number of manitenace catch up items and some repairs.
Thanks in advance.
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Old 05-08-2011, 05:28 PM   #2
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Our 78 had numerous 'wire nuts' used to make 12 volt connections in the o'head wiring - don't know if AS did it or a PO...

Using wire nuts are a big no-no, IMHO, especially for low voltage wiring!

If you happen to be cursed with wire nuts, it's possible one has come loose during you're fan repair...

I think you're only hope is to use a DC volt meter and begin tracing from the Univolt back to the fan POS feed wire...

The POS goes from the Univolt to the 12 volt fuse distribution panel - carefully check each leg of the journey from the Univolt (hopefully the new fuse fixed that problem) to the fuse panel, then on both sides of the fuse that feed the rear fan (and other items)...

An AS wiring diagram of the low voltage system would be helpful...

If you have 12 volts out of the fuse panel on the fan circuit, you'll have to check the overhead wiring -

Assuming that your 12 volt fuse panel is mounted in the front of the trailer - check the front o'head vent ass'y, remove the fixture inside to gain access to the 12 volt wiring - you can usually then see the bundle of wires o'head, as well as the connections to that vent/light and see if you have 12 volts at that location - check the connections carefully, making sure they are clean, bright and tight - used new crimp connectors if required, cutting back the wire ends if necessary to get to some clean, bright wires for a good connection...

If your 12 volt fuse panel is mounted in another location (not at the front), you'll have to find out where the fused circuit wires go from there, to properly check for continuity...

After checking the fwd vent, with still no power at the fan, you'll have to go to the next vent/light assembly and repeat the operation of checking the wires and connections, etc...

You might be able to check the 'color' of the POS feed wire back at the fan and look for that color wire each time you look at the o'head wires - you could use one of those automotive testers that have a sharp needle point to push into the wire to see if it's 'hot' - 12 volt POS - along the way...

Those old fuse panels have a way of hiding bad conducting fuse connections - I'd remove all the fuses, one at a time to check them for continuity, and also make sure that they 'seat' into the connectors without any tarnish to insulate the circuit - you can also use your volt meter on each side of the fuse to make sure the connection is good - I like to remove and re-seat all the fuses when there's a problem...

Hope that helps...
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Old 05-08-2011, 05:32 PM   #3
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Do you have a voltmeter or a 12v test light? If the power supply is good you should see 12v (or a light) when you probe either end of a good fuse (other lead to ground). If you get 12v on one end only, the fuse is bad. If you get 0v then you need to diagnose the univolt. If you get 12v on both ends of the fuse but nothing at the fan/light there may be another fuse in between. A 30a fuse seems big for a light circuit. Look to see if you have another lower amp fuse blown.
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Old 05-08-2011, 05:57 PM   #4
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Thanks for all the hints. Perhaps I should add that the fuses are in the univolt. The fuse that blew fed a large blue, about 10 guage that disappears into the wall, which makes me think it goes to another fuse panel??where?. I have checked the all fuses and all are ok.
Any other ideas?
There are a lot of wire nuts. Why are nuts bad on 12v, I didn't know this?
The univolt is under the rear bath sink, is there another panel up front somewhere?
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Old 05-08-2011, 06:07 PM   #5
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OK, your 12 volt system is the reverse of ours - our Univolt was in the front, with the 12 volt fuse panel nearby, a couple of feet away...

Where are your batteries located? I would think the 12 volt fuse panel would be nearby, but maybe not...not familiar with your 79 model...

You should have some kind of 12 volt fuse panel with 8 - 10 individual tubular glass fuses - unless a PO has changed things around...if you have multiple fuses mounted on the Univolt, perhaps the panel was 'integrated' in your trailer and not separate - the heavy 12 volt wires would then be routed to the batteries...???

Do you have a wiring diagram for your trailer? That would give you lots of info for this kind of problem...

Working on an older trailer can be a 'lifetime' of 'adventure'...
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Old 05-08-2011, 06:13 PM   #6
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The battery is accessed from outside but only about a 3-4 foot run from the univolt. Can't find any old type glass fuses or any sub fuse panel other the one in the univolt. I do have a DC meter and as I said there is power going to that large blue wire disappearing into the wall, it has to branch off somewhere as the fixtures that are not working only have 2 smaller guage wires going to them, no power at the fixtures.
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Old 05-08-2011, 06:30 PM   #7
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You'll have to try and 'follow' those two heavy wires from the Univolt - they must go to the fuse panel...

On our 78, the battery cables AND the univolt cables are connected to same fuse/distribution panel...

You've got a fuse panel in there somewhere - can you trace the cables from the batteries to the fuse panel? The panel has to be close as the batteries are also close to the Univolt...

Where's Sherlock Holmes when we need him?
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Old 05-08-2011, 07:11 PM   #8
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Mexray,
Thanks for your input, what you said about a PO made me think to look up front, found the old glass fuses, but shucks, none were blown. Tested and I am getting 12v up there across the fuses.
I took apart 2 of the none working fixtures to see if there was a junction up there, none so far, have one more I can do. That's where I've been the last few minutes. Running out of places to look. Keep thinkin and suggestin, thanks.
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Old 05-08-2011, 07:35 PM   #9
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Sometimes the sub fuse panel is hidden behind a fabric wall snap on panel. I had a 79 Excella and now an 85 and the fuse panel and univolt are at the front close to the batteries.
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Old 05-08-2011, 09:14 PM   #10
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Thanks to all, I have still not found the trouble. Must keep looking, but sure is frustrating. Keep telling myself, wanted a project!
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Old 05-09-2011, 07:08 PM   #11
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All,
Many many thanks! Ayyup!! the lights are working! Through everyone's ideas and encouragement, found the trouble. As suggested I had checked the fuses many times, all looked ok, DC meter showed current going through, I thought, maybe I was touching another fuse while testing.
Anyway, the trouble was a fuse that looked ok. Today I took them all out, again, but this time checked them for continuity one by one. Found one that tested bad even though it looked good.
I'm sure the pros would have done that, but maybe that is a lesson I can share with others (maybe not too many as dense as me) that testing fuses while not plugged in maybe worthwhile when everything else seems ok, maybe should start here.
Again, thanks everyone.
It was a wicked good time.
Dan the Stumpjumper
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Old 05-10-2011, 11:37 AM   #12
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Once again persistence pays off. Be assured you're not the first to have been bitten by a fuse that looked good.
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