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Found the Gremlin, Wiring Damage

January 27, 2018, 08:10:19 pm

Found the gremlin.  When I bought my GV the PO mentioned that you had to pull the fuse for the gauges when parking the coach or the engine battery would run down.  I figured, okay, just a minor electrical issue, I can handle that.  Then I found the receipt for several hours of electrical troubleshooting at an RV shop, with a note at the bottom, "problem not resolved".  Further digging found the wrong alternator had been installed and a lot of hacking and splices in the wiring in the engine compartment.  Testing identified that somehow the gauge circuit was being back fed from the alternator sense lead.  Finally, I discovered the ignition contactor in the dash was making the right noises, but not actually working, so dash loads were also pulling through the gauge circuit from the sense lead.  Today, I found the underlying cause.  Somehow, someway, the alternator sense lead had been subjected to a significant current.  I suspect a direct short to ground when the wrong alternator was initially installed.  It got so hot much of the insulation melted and a portion of it fused to the hot side of the water temp sensor wiring and connected those two circuits.  Apparently the installation error was noticed and removed, but the damage was not realized.  Some work had been done of the wiring harness, but the actual problem was overlooked.  The work that was done was shoddy, the wrong gauge and wrong color wires were used, no heat shrink, as well as a wire nut.  Also at some point the wiring to the hour meter partially melted against the exhaust system.

Tomorrow's project is to replace the damaged wires, and rewire the existing splices with correct color and gauge wire, and heat shrink the splices.  Once that is done I can install the new Kilovac contactor, the new Delco alternator with the sense lead, and the new hour meter.  I am still waiting on the new headlight switch.  Hopefully that will resolve the primary issues.

Anyway, here is what wiring should not look like:

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Re: Found the Gremlin, Wiring Damage

Reply #1 – January 27, 2018, 09:31:48 pm

Can anyone think a reason not to add a weatherproof fuse holder between the isolator post and the alternator sense wire?  This is an unprotected circuit, and a short on this lead seems to me to be a potential coach killer.  Would there be enough voltage drop across a fuse to affect the output of the alternator?

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Re: Found the Gremlin, Wiring Damage

Reply #2 – January 28, 2018, 09:36:01 am

Mike  ----  Voltage drop across the fuse would be insignificant.  What I would be concerned about would be that since it is not done by builder that the fuse would not show up any where and would be forgotten.  I would add it to your schematic, if you have one,  and /or flag it some way so that it is noticeable.  You may need to do a little home work to decide what size of fuse to use.  Have a great day  ----  Fritz

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Re: Found the Gremlin, Wiring Damage

Reply #3 – January 28, 2018, 09:38:26 am

Good find.

I see no problem with a waterproof fuse holder-- just need to verify that there is not a voltage drop across it.

But, have never heard of a failure in that wire caused by over-current, so suspect you are correct about cause.  If full alternator output were put on that small gauge wire, presto it severely overheats.

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Re: Found the Gremlin, Wiring Damage

Reply #4 – January 28, 2018, 07:13:04 pm

I think what actually happened is when they installed the wrong alternator they wired the sense lead to one of the diode studs.  I noticed the center one only has a single nut, while the outer ones are double nutted.  If the batteries were disconnected when the alternator was installed they would not realize they had actually wired the sense lead to ground.  The spark when reconnecting the batteries was not recognized, but when the harness on top of the engine started to melt they discovered the problem.  Unfortunately they did not realize the extent of the damage and only repaired the wiring on top of the engine.  They then ad libbed a connection from the compromised sense lead to the voltage regulator.  They are lucky the coach didn't catch fire.

I didn't get it all back together today, but at least the crawling under the coach part is finished.  I still need to trim the new sense lead to length at the engine, redo the splices in the water temp sensor and the engine on sensor, reassemble the harness loom, then install the new alternator.  I did get the new hour meter and ignition relay installed.  This visibly raised the voltage on the voltmeter, speed up the wipers, and caused the right side remote mirror to start working.  The old relay was actuating but sometimes not conducting, all the power was going through the damaged sense lead and hour meter feed wires.  It's a miracle it worked at all.

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Re: Found the Gremlin, Wiring Damage

Reply #5 – January 28, 2018, 08:29:17 pm

Great job. I wish I could figure out circuits like that!
Dick

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Re: Found the Gremlin, Wiring Damage

Reply #6 – February 03, 2018, 03:51:10 pm

Well, that took longer than expected.  I took Friday off and spent the day with the coach.  I installed the new headlight switch, completed the wiring harness repairs, and installed the new Delco 28SI alternator.  Got it all buttoned up about 5 PM and cranked it up.  No charging!  By that point I was too tired to look at it anymore, so I called it a night.  I did a little poking about on the forum and the web, and started to suspect the battery isolator.  This morning I went back down and discovered all the diodes in the isolator are open.  They don't conduct in any direction from any position.  I moved the alternator lead to the engine battery connection and started it back up again.  Bingo!  Battery voltage climbed immediately and we were charging.  That was enough to get it down for its state inspection so I can finally get it registered.  While driving I flipped on the boost switch as a kind of manual isolator to charge the coach battery, then switched it off when I shut the engine down.  For now that gets it done, but of course we aren't using the coach.  It is plugged in on two small battery maintainers, the breaker for the original power converter is switched off.

Now I get to select and install a new isolator, but at least the pressure is off now that the inspection is done.  I suspect the isolator was the original problem, misdiagnosed as a bad alternator.  That started the whole chain of disasters, wrong alternator, wiring damage, and so on.  I wonder if the PO would have sold the coach if this hadn't happened.  Installing a new isolator is a great opportunity to move it to a drier location, so that is in the cards.

BTW, while reviewing the Delco 28SI install instructions it called for a 5 amp fuse in the battery sense lead. 

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