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Old 02-11-2014, 07:17 PM   #1
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1972 Argosy 20
Snoqualmie , Washington
Join Date: Sep 2012
Posts: 379
Blowing 30A Fuse, 7 pin challenged

Bear with me on this
When I purchased our 72 Argosy, the PO had installed a new Pollack 7 pin connector and told me he had left the blue battery charging wire capped off because he felt it would drain the TV battery if left connected. I replaced the Univolt with a Power Dynamics 9245 and re-used the old fuse panel, and hooked up the capped off battery wire inside the umbilical chord Pollack plug.
Everything works - turn signals, brakes, brake lights, running lights, all interior lights, etc.
However, the 30A fuse on the blue wire marked on the fuse panel as "tow vehicle" occasionally blows. I've attached a photo of the fuse panel. Any thoughts on what would cause this?
The second issue I have is that when I put my voltage tester on the Pollack plug at the trailer end, I get 13.2v when I touch position #1 (per the attached Pollack detail) with the red lead and the #7 (center) pin with the black lead. When I touch #1 with any other pin, nothing. This is most confusing to me. I had hoped to be able to rig up a jumper to have the running lights on for short periods while in camp per this thread
I'm concerned about the the issue of blowing a 30A fuse, and I guess the wiring at the 7 pin connector is more of wanting to understand how and why things work. Anyway, I would appreciate any feedback on this.
Sorry for the longish post
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Old 02-11-2014, 11:21 PM   #2
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SW , Missouri
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Since you said that everything works, I'm assuming that you have standard wiring at your tow vehicle's 7-pin plug. Wire colors from older Airstreams do not match the modern tow vehicle usage.

I have attached a file with the Airstream colors and service descriptions that may help you in your trouble shooting. This is house side wiring only and may not be applicable depending on what the PO did.

The ideas below reference the pin #'s in the Pollak diagram you attached.

The first issue:

If the fuse blows randomly, you probably have an intermittent short. It's possible that you have wires contacting within your 7-way plug where you have connected the formerly capped wire. This is unlikely, but when I'm trouble shooting electrical problems, I always start with the last thing that I messed with.

The second issue:

#4 is the positive line from your house battery /12V when disconnected from your tow vehicle. If you use a volt meter across #4 and #1 it should read the battery voltage. This would be approximately 13.2V if you are on shore power and your converter is in float mode. Checking the voltage between #1 and any other pin should be 0V since #1 should be the ground.

To have your running lights on, you want to jumper #4 to #3. If you jumper #4 to #1, you will blow the 30A fuse as you just created a dead short.
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File Type: pdf 7wayplug1966-81.pdf (9.0 KB, 55 views)

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Old 02-11-2014, 11:47 PM   #3
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Grand Junction , Colorado
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Dry, the pin pattern you included on your post is for a different pattern than you appear to have. The one Kyle attached appears to be the right one for your truck and trailer. If the center pin on yours is hot (charge line), then using the other lead from the voltmeter to any ground including the truck bumper should read about 13.2 v. Regardless of what pin is ground, check against bare metal on the truck as well.

The previous owner was wrong about the charge line draining the truck battery. When the truck is off, the charge line is cut off by a relay and the battery is not drained. You have to test with the truck running.

If you are sometimes blowing a 30 amp fuse, maybe you have the two different pin configurations confused and have created a short when you step on the brakes or turn on the lights. I haven't really worked this out to see what mis-combinations will cause what problems, but I would look at that possibility to make sure that is not what is creating that problem.

I agree with Kyle—check the last thing you did to see if you didn't cause the problem unknowingly. Also, the answer is usually the simplest thing and hopefully the cheapest.

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Old 02-12-2014, 12:51 AM   #4
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Hi, when you say that the fuse blows, do you mean that the fuse burns in the middle making an open circuit? Or do you mean that the fuse looks OK but becomes an open circuit? Looking at your picture, it looks like the blue wire has changed color at the fuse panel. Also the connection at the blue wire looks dark to me. If this is the case, you have a dirty / corroded fuse holder that will cause high resistance, which causes a lot of heat. This will cause the solder on the end of the fuse to melt, making an open circuit. This is not considered a blown fuse. It is a melted fuse. If this is the case with your trailer, You need to clean the fuse holder, replace the fuse holder, or by-pass it with an in-line fuse holder.

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Old 02-12-2014, 06:39 AM   #5
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Just an observation w/o the benefit of looking into the problem first hand.

Kudos to Kyle, Gene and Robert.

Those are some darn fine suggestions and starting points, well worth somebody buying a round just for the clean effectively presented comments.

And that connection box and wiring diagram, nice setup and Robert picking up the color change on the insulation very observant.

Sparks are in your court DryFly.

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Old 02-12-2014, 08:18 AM   #6
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1972 Argosy 20
Snoqualmie , Washington
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Thanks to you all, as always. I'll be looking at this starting Sunday and will report back. Robertsun - the fuse burns in the middle. I've considered replacing the fuse box, but once I had it installed I became rather sanguine about it. Maybe its time to just do it.
Great suggestions.
Thanks again
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Old 02-12-2014, 09:29 AM   #7
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South of the river , Minnesota
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Hello DryFly

There are three possibilities at work two of which have been pointed out by others:

1) Something is miswired
2) There is an intermittent short.

But there is a third possibility that they haven't counted upon which is:

3) The current in the charge circuit sometimes exceeds 30a.

It is not uncommon for this to occur and there are two possible causes.

First, it is possible for the batteries in the trailer to charge at more than 30a, particularly if the batteries are fairly new and deeply discharged.

Second, if you have a weak/older battery in your tow vehicle, and fully charged batteries in the trailer, it is possible to have more than 30a flow in the "reverse" direction during engine starting or if the alternator is failing.

In order to understand what's really going on you have to connect an ammeter. There are clamp-on and wire-in ammeters available. I have a charge-line ammeter permanently installed in my truck camper and have thought about doing something similar in my trailer or the tow vehicle I use for it.
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Old 02-12-2014, 08:04 PM   #8
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1972 Argosy 20
Snoqualmie , Washington
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Posts: 379
Well I couldn’t wait until this weekend, so I had to fuss with it. I got thinking about the basic tenant that “something is wired wrong” (thanks Jammer, I couldn't sleep after reading that!). I got out my multi function voltage meter and mapped the truck’s 7 pin connector, then checked out the trailers end. Turns out that the PO had placed the ground wire in the position where the battery wire should have been. This wasn’t a problem until I decided to re-connect the battery wire to the empty space on the Pollack plug. Once that was done, the battery charging system from the truck was feeding 12v power (I guess) back to the ground. Thankfully, the 30A fuse sacrificed itself (did its job) every time I hooked up the trailer to the truck.
I guess that when I said “everything works”, that really didn’t mean that “everything is OK”. Yes the turn signals, brakes, brake lights and running lights worked when hooked up to the truck, but the whole system wasn’t correct. I wonder what kind of issue I could have experienced on the road. Certainly my battery would have died an early death while boondocking because it wasn’t being recharged while towing. What else? I don't like the thought of a 30A fuse blowing and not knowing why.

Anyway, I’ve attached a modified drawing showing what I really have (now that it’s all connected correctly) for someone’s future reference. As always, I learned a LOT working on this issue, especially because of the input from all of your suggestions.
And, if our paths cross, I will happily buy each and every one of you a fine IPA as a modest repayment.
This forum is such a great resource – how fortunate we all are. Here’s the corrected drawing of my actual hookup.
Attached Files
File Type: pdf Argosy Umbilical Wiring Actual.pdf (21.0 KB, 39 views)
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Old 02-12-2014, 08:28 PM   #9
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1972 Argosy 20
Snoqualmie , Washington
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Posts: 379
BTW, great catch on the discoloration of the blue wire at the fuse box. That comment is what really got me concerned. I do think I was over loading the wire for a short period before the fuse blew. I don't know when this happened, but as previously posited, probably when I stepped on the brakes or used the turn signal.
Thanks again all

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