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Old 08-16-2024, 09:24 AM   #1
Mini-Skoolie
 
Join Date: Oct 2021
Location: New England
Posts: 33
Year: 2005
Coachwork: Corbeil
Chassis: GMC Savana 3500 Dually
Engine: 6.0 Gas V8 > GMC/Chevy
Rated Cap: 14 - 12,500 GVWR
Mystery fuse keeps popping to a no-start after sitting

Hey Gang,

I've got a 2005 GMC Savana 3500 with a Corbeil 5-window, 6.0 gas.

After many hours of fixing this thing up, it finally runs fantabulously -- when it decides to run. There is a non-factory-looking mystery fuse connected to a relay just above the master cylinder under the hood (I'll provide a pic soon). While we're still building out the interior, the truck sits on ramps for long periods. I try to start every week, but sometimes life gets in the way, and it's a couple of weeks between starts.

Thinking the battery was dying, I put it on a charger, but it still didn't work. So I found that that fuse, a 10A, had blown. So I replaced it, happened again a couple of times over a few months. Then I noticed the fuse holder itself was corroded. So I cut that one out, replaced it with a new one, cleaned the wiring, etc., but it happened again last night.

I went to start it, got one single click, threw it on the charger, then no click. So I checked the fuse again and sure enough, toast.

Because Corbeil is defunct, I can't get the wiring diagrams and even if I could, this thing looks like a non-factory setup. We did remove several pounds and about 8,000 miles of unneeded wiring, but this was happening before that. When the fuse is fresh, it starts right up and runs great. No wiggles, no shimmies, no nothing but smooth V8 sounds. All other functions work as normal with key on, pre-start.

Wondering if it pops only when I try to jump it (who invented side post batteries anyway, for cryin' out loud). Does anyone have a similar set up that can tell me what this thing is and where it goes? Seems to disappear in the engine bay.

Cheers
Attached Thumbnails
Mystery Fuse Location 081624F.png   Mystery Fuse Top 081624F.png   Mystery Fuse Front 081624F.png  

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Old 08-16-2024, 12:29 PM   #2
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Year: 1999
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That was a very detailed explanation that really explained ...not so much...

Have you followed the wires to see where they go?

That would be first step of troubleshooting 101.....
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Old 08-16-2024, 12:40 PM   #3
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As of 2002 Corbeil started installing Pran multiplex systems in their mini busses.

what this means is that you should not cut wires unless you know, not guess, what your are doing.
sorry if I sound mean but this is what happens.....

By using the search feature, which you should also, I found a thread that has some links for Corbeil bus wiring.

https://www.skoolie.net/forums/searc...archid=5958281

It is in post #2 of this thread.

https://pransystems.com/en/products/all/page/1/

Good luck !
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Old 08-16-2024, 01:04 PM   #4
Mini-Skoolie
 
Join Date: Oct 2021
Location: New England
Posts: 33
Year: 2005
Coachwork: Corbeil
Chassis: GMC Savana 3500 Dually
Engine: 6.0 Gas V8 > GMC/Chevy
Rated Cap: 14 - 12,500 GVWR
Hey, thanks for the response -- and I don't think it was mean. I did actually find those links, but unfortunately, they are much too small/pixelated/blurred to see everything I needed to see.

I have not yet followed those wires into the dash. The post was more of hoping for a quick, "Yes, I know what that is and where it goes" before I ripped apart the dash again. I belong to another forum that has a section where people can sort of hold up a part and say 'what's this thing?' and people chime in with their best guess.

Also, as previously mentioned, this condition was happening prior to any de-wiring, which we did very, very methodically. I also didn't mention, that our bus was a former prep school bus, so it did not come with any flashers, swinging stop signs, heated mirrors, roof escape hatch, etc. However, the bus did contain all the wiring for those things, even for the wheelchair lift, warnings, etc., but our bus doesn't even have the wheelchair door. So, one by one, or harness by harness, we eliminated wires and started the bus and tested everything after each removal. The only the only switches on the keyboard were for the overhead dome lights and the aux heater.

Those 'mystery fuse' connections also do not look factory from either GMC, or Corbeil. It was definitely previously monkeyed with before we picked it up. The fella who had it before was using it as a sort of mobile greenhouse, so who knows.

Anyway, thanks for the reply. Perhaps I'll have another gander at those drawings and see if I can pull anything out!
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Old 08-16-2024, 01:52 PM   #5
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Join Date: May 2018
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my recommendation

follow the wires. that wire
1) has power and damaged insulation, that is why the fuse is blowing. called "short to ground.

2) The load normal for that circuit is more than 10 amp AND has the wrong fuse- look at the size of wires. Is the wire size correct for 10 amps?

3) the fuse and circuit is functioning as designed and you need to figure out what is connected to the other end.

4) a combination of the above three items.

my gut reaction is number one. electrical failures are the most time consuming repair work I have ever done.

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Old 08-16-2024, 02:20 PM   #6
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just looked and my 2004 express does not have that fuse?
mine is a collins body and everything runs through a fuse block one under the hood
one under the drivers seat and one installed by collins in a compartment above the dash.
as mentioned that wire is shorted out somewhere.
wrong size fuse for the load or if its for a fan motor somewhere auxiliary heater or something the motor could be powered and hung up?
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Old 08-16-2024, 02:33 PM   #7
Mini-Skoolie
 
Join Date: Oct 2021
Location: New England
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Year: 2005
Coachwork: Corbeil
Chassis: GMC Savana 3500 Dually
Engine: 6.0 Gas V8 > GMC/Chevy
Rated Cap: 14 - 12,500 GVWR
Thank you William! I will check out those options tonight. I was wondering about the fuse size, but I just replaced with what was in there by the previous owner. I'll check to the wire-gauge-to-fuse-size as well. Any/all those options make sense. Thanks!
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Old 08-16-2024, 02:38 PM   #8
Mini-Skoolie
 
Join Date: Oct 2021
Location: New England
Posts: 33
Year: 2005
Coachwork: Corbeil
Chassis: GMC Savana 3500 Dually
Engine: 6.0 Gas V8 > GMC/Chevy
Rated Cap: 14 - 12,500 GVWR
Yeah, I definitely think it was played with before. My understanding is Collins bought out Corbeil, but not sure if anything carried over. I do have the under-hood fuse block, under-seat fuse block, and also that overhead block, but mine only had a couple of fuses in it because it didn't have any of the traditional 'school stuff' in it. Thanks for looking at yours, much appreciated! I'll see what I can find out tonight. Here's hoping the short's under the hood and not the dash!


EDIT: We took out the aux heater under where the seats were and also took out the coach-side AC, so both fans went away with those.
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Old 09-20-2024, 10:57 AM   #9
Mini-Skoolie
 
Join Date: Oct 2021
Location: New England
Posts: 33
Year: 2005
Coachwork: Corbeil
Chassis: GMC Savana 3500 Dually
Engine: 6.0 Gas V8 > GMC/Chevy
Rated Cap: 14 - 12,500 GVWR
Found it! Finally.

Hey Gang,

Thanks again for all the responses, much appreciated!

I finally found the Purple Menace.

After tracing and testing and testing and tracing, I pulled the under-hood fuse block and took it all apart - all 5+ layers of the thing. Looked clean and neat and not an issue. I guess on some GMC's, water gets in and connections 'grow' to other connections with corrosion and the like.

Didn't happen in this case, but as I was about to reinstall, I found that one of the harness connections to the computer, which, in GMC's infinite wisdom is mounted on the inner fender wall where all the rain and salt goes, was resting against a rusty bolt protruding in from the hawkeye mirrors.

When I pulled it out by hand, I initially didn't see/feel anything. Just for shits and giggles, I put a little mechanic mirror behind it and sure enough, I found that the rusty bolt had worn away and corroded the starter igniter/exciter thingamabob and was shorting out.

So I spliced in a new section of wire, harness wrapped that, and put it in two casings of split loom. For good measure, I had a spare brake caliper bleeder screw rubber protector, so I ziptied that to the end of the rusty bolt.


Hopefully that'll last another 19 years!
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Purple Menace Wire Cut.jpg  
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Old 09-20-2024, 06:51 PM   #10
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Join Date: Apr 2020
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Chassis: Ford E450
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maddening that it could be so hidden, but you illustrate exactly what is needed in this skoolie conversion business-you have to be very, very thorough, dig all the way down to the bottom, inspect every inch, investigate every anomaly, be systematic, follow the guidebook, use your common sense, don't cut corners, and give it an extra sanding just to be sure.

Otherwise, mileage will vary!
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Old 09-20-2024, 08:31 PM   #11
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Join Date: Mar 2021
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Quote:
Originally Posted by Rucker View Post
maddening that it could be so hidden, but you illustrate exactly what is needed in this skoolie conversion business-you have to be very, very thorough, dig all the way down to the bottom, inspect every inch, investigate every anomaly, be systematic, follow the guidebook, use your common sense, don't cut corners, and give it an extra sanding just to be sure.

Otherwise, mileage will vary!
Zackly, Rucker!

Every inch of wiring needs to be investigated when problems arise.
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