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Short in the ACC pole

Tom_Barb
Explorer
Explorer
Our motorhome 2002 Newmar Mountain Aire, 8.3 cummins has a short in the Accessory side of the ignition circuit.
When you replace the fuse, and turn the key to ON- or - Acc, the fuse blows.

The ignition switch has been replaced. ---- same results
all circuits for the Accessories have been disconnected. --- still blows the fuse
Connecting the fuse to the ACC pole of Ignition switch and the fuse (+) show continuity.

The Cummins computer tool will not turn on, it requires the ignition to be turned on, which blows the fuse.
All the relays In the coach have been tested all fuses and been checked.

due to the dead engine the air is depleted "0" so the breaks are locked.
2000 Newmar mountain aire 4081 DP, ISC/350 Allison 6 speed, Wrangler JL toad.
22 REPLIES 22

MrWizard
Moderator
Moderator
If you have the schematic that shows which items are powered via that fuse
Remove fuse check continuity to ground from that feed to ground,
Now the slow part, one by one disconnect each item until you find the one that makes your continuity short disappear
I suspect that something has failed, something that would automatically have power, not something you are going to manually b operate a switch for,
Unless you have had a rodent chewing on wires, that should be visible unless it chewed a random spot In harness somewhere, creating a short between that hot feed and the ground lead for something else
How long as it been parked
I can explain it to you.
But I Can Not understand it for you !

....

Connected using T-Mobile Home internet and Visible Phone service
1997 F53 Bounder 36s

Tom_Barb
Explorer
Explorer
Flute Man wrote:
. Exactly what fuse is blowing?
Jerry
And what size is the fuse? How many amps?


It is labeled " 15 Key SW' and it is a 15 amp

It is in the #1 junction box.
2000 Newmar mountain aire 4081 DP, ISC/350 Allison 6 speed, Wrangler JL toad.

dougrainer
Nomad
Nomad
Tom/Barb wrote:
dougrainer wrote:
Lets get clear.
1. You state the IGN system. You mean it does NOT short until you turn the key all the way to engage the starter?
2. The Ign controlled COACH systems including Dash Area(Back up and so on) all work even when the other fuse blows? Doug


The key switch excites both the ACC and the IGN at the same time. when the key is turned to either position, then you turn to IGN and continued to turn to crank.

the fuse blows as soon as either position is reached.

this is why I say there are two discrepancies.


Yes and No. When you turn to IGN(NOT the spring loaded Starter position) it activates Both ACC side and Ign side circuits. BUT, when just going to ACC, that position activates fewer circuits than the IGN side, BUT, will still activate the 1 circuit that blows the fuse. ONE problem, for both sides. Once you find and fix the short, BOTH sides will work and not blow the fuse. Lets wait until you do your ECU testing. So, you refuse to doublecheck the batteries? Doug

Flute_Man
Explorer
Explorer
Generally, there is only one fault. However by replacing disconnecting and reconnecting all those other things you can accidentally induce another fault. Exactly what fuse is blowing?
Jerry
And what size is the fuse? How many amps?
Jerry Parr
05 Mandalay 40B
Cat C7 350
04 Honda CR-V
Ham Radio K7OU
Retired EE
Jrparr32@gmail.com
602-321-8141
Full-timer

Tom_Barb
Explorer
Explorer
dougrainer wrote:
Lets get clear.
1. You state the IGN system. You mean it does NOT short until you turn the key all the way to engage the starter?
2. The Ign controlled COACH systems including Dash Area(Back up and so on) all work even when the other fuse blows? Doug


The key switch excites both the ACC and the IGN at the same time. when the key is turned to either position, then you turn to IGN and continued to turn to crank.

the fuse blows as soon as either position is reached.

this is why I say there are two discrepancies.
2000 Newmar mountain aire 4081 DP, ISC/350 Allison 6 speed, Wrangler JL toad.

dougrainer
Nomad
Nomad
Lets get clear.
1. You state the IGN system. You mean it does NOT short until you turn the key all the way to engage the starter?
2. The Ign controlled COACH systems including Dash Area(Back up and so on) all work even when the other fuse blows? Doug

Tom_Barb
Explorer
Explorer
dougrainer wrote:
Then see if you have the short? Doug

The ignition switch is out of the system. What is tripping the short is the IGN pole.

The coach system is on a circuit board, all coach systems are routed thru that circuit, That was been changed, no difference.

The Spartan circuits in the coach operate normally, the only thing that is wrong is the IGN system.
all signal lights work, back up camera, all external lights work.

Spartan's skit, shows a direct circuit to the Transmission computer and the ECU, the Transmission computer that has been disconnected. still shows a short.

I'm in process disconnecting ECU.

stay tuned
2000 Newmar mountain aire 4081 DP, ISC/350 Allison 6 speed, Wrangler JL toad.

dougrainer
Nomad
Nomad
I am telling you to go at the problem from the Newmar COACH side of the electrical. Have you pulled the Batteries to verify you did not miss a wire or disconnect the smaller gauge wires from both the chassis batteries and the coach batteries. DON'T TELL ME YOU HAVE DONE THAT WHEN YOU HAVE NOT. I have had over 42 years customers swear they have doublechecked after they replaced batteries and they have either a short or a system does not work. They come in and in less than 10 minutes I find the loose wire or POS small gauge wire connected to the negative or a loose wire the batteries were installed on and after awhile, the weight has cause a short. Then they pay me about $100 because they were positive they had done it correctly. On your year, do you have some of the interior ceiling lights that has a 3 position wall switch? When engaged one way the lights are normal brightness and when switched the other way they have 50% dimmer brightness? Did your original Coach batteries, were they 6 volt(making 12 volt) or 12 volt and which do you have now, 6 volt(making 12 volt) or 12 volt. Last, did you do as I suggested and disconnect the small gauge wires both Neg and Pos from the Battery banks and leave just the Heavy duty large Cables connected? Then see if you have the short? Doug

Tom_Barb
Explorer
Explorer
dougrainer wrote:

READ my post again. As I stated, you are(were) looking at the problem from a chassis standpoint. Doug


After removing the entire ACC side of the system. it now becomes clear that the ACC side is not the problem.

next step? Separate one system from the other by Disconnecting the ECU from the engine, see if the short goes away.

working on it. 🙂

It is not a easy place to get to. To touch the ECU the fuel filter must be removed.
Edit
There is two ECMs for the IGN, side of the Engine system, the Alison / transmittion
The Transmittion is easy , (done) we still have a short.
2000 Newmar mountain aire 4081 DP, ISC/350 Allison 6 speed, Wrangler JL toad.

Tom_Barb
Explorer
Explorer
Flute Man wrote:
Was there any incident just prior to it not working?
Jerry Parr

No, We parked the Coach and now it won't crank, and blows the fuse.
2000 Newmar mountain aire 4081 DP, ISC/350 Allison 6 speed, Wrangler JL toad.

dougrainer
Nomad
Nomad
Tom/Barb wrote:
Matt_Colie wrote:
Tom,

I have done diagnostics on systems that looked a lot like your situation. I am guessing that the ACC circuit comes out of a gang plug on the ignition switch...
If that is the case, can you identify that wire?
If you can, remove that wire from the gang plug. This is just about always possible, but it is never easy (we seem to be way past easy) and it may take a special tool to release the latches that hold that connector in the plug body. When it is loose, now at least you can power things up and fine out what is not working. That may lead you in the direction you need to go.

Now that the system does not blow the main fuse, it might blow a single fuse for a single part of the ACC system. This could be your bast bet to track down the problem. You can now get things started.

Next cheap, dirty and very effective search method.
Now that the problem circuit is isolated, feed it power through a good sized light bulb. I have a collection of bulbs with wire leads attached but I do this more than most people. When powered up that light should light up - if there is the solid ground you reported.
Now here comes the simple and cheap part. Get a small compass. The current in that wire is creating a magnetic field that you can follow. You won't be able to follow it when it is inside the frame rail, but any place that wire is exposed, you should be able to identify it.
Sorry, I had to put a break in here.
The compass needle will lead you along. Just keep looking for the indication of current flowing, when you no longer get that, the short to ground is behind you.

Please keep us informed what you find or don't. Everything matters.

Matt
Your compass trick, is a tone generator. I have traced the "10-Green wire that will emit a tone until I can no longer get to the cable bundle. then it comes in rear, there is no Green "10" wire.

I suspect there is two discrepancies. and I may confuse the issues.
Today I removed 12v power to the ACC pole in the ACC junction box, This disables the entire ACC accessories. It still blowed the fuse, I have been barking up the wrong tree.
tomorrow we try again.


READ my post again. As I stated, you are(were) looking at the problem from a chassis standpoint. Doug

Tom_Barb
Explorer
Explorer
Matt_Colie wrote:
Tom,

I have done diagnostics on systems that looked a lot like your situation. I am guessing that the ACC circuit comes out of a gang plug on the ignition switch...
If that is the case, can you identify that wire?
If you can, remove that wire from the gang plug. This is just about always possible, but it is never easy (we seem to be way past easy) and it may take a special tool to release the latches that hold that connector in the plug body. When it is loose, now at least you can power things up and fine out what is not working. That may lead you in the direction you need to go.

Now that the system does not blow the main fuse, it might blow a single fuse for a single part of the ACC system. This could be your bast bet to track down the problem. You can now get things started.

Next cheap, dirty and very effective search method.
Now that the problem circuit is isolated, feed it power through a good sized light bulb. I have a collection of bulbs with wire leads attached but I do this more than most people. When powered up that light should light up - if there is the solid ground you reported.
Now here comes the simple and cheap part. Get a small compass. The current in that wire is creating a magnetic field that you can follow. You won't be able to follow it when it is inside the frame rail, but any place that wire is exposed, you should be able to identify it.
Sorry, I had to put a break in here.
The compass needle will lead you along. Just keep looking for the indication of current flowing, when you no longer get that, the short to ground is behind you.

Please keep us informed what you find or don't. Everything matters.

Matt
Your compass trick, is a tone generator. I have traced the "10-Green wire that will emit a tone until I can no longer get to the cable bundle. then it comes in rear, there is no Green "10" wire.

I suspect there is two discrepancies. and I may confuse the issues.
Today I removed 12v power to the ACC pole in the ACC junction box, This disables the entire ACC accessories. It still blowed the fuse, I have been barking up the wrong tree.
tomorrow we try again.
2000 Newmar mountain aire 4081 DP, ISC/350 Allison 6 speed, Wrangler JL toad.

Matt_Colie
Explorer
Explorer
Tom,

I have done diagnostics on systems that looked a lot like your situation. I am guessing that the ACC circuit comes out of a gang plug on the ignition switch...
If that is the case, can you identify that wire?
If you can, remove that wire from the gang plug. This is just about always possible, but it is never easy (we seem to be way past easy) and it may take a special tool to release the latches that hold that connector in the plug body. When it is loose, now at least you can power things up and fine out what is not working. That may lead you in the direction you need to go.

Now that the system does not blow the main fuse, it might blow a single fuse for a single part of the ACC system. This could be your bast bet to track down the problem. You can now get things started.

Next cheap, dirty and very effective search method.
Now that the problem circuit is isolated, feed it power through a good sized light bulb. I have a collection of bulbs with wire leads attached but I do this more than most people. When powered up that light should light up - if there is the solid ground you reported.
Now here comes the simple and cheap part. Get a small compass. The current in that wire is creating a magnetic field that you can follow. You won't be able to follow it when it is inside the frame rail, but any place that wire is exposed, you should be able to identify it.
Sorry, I had to put a break in here.
The compass needle will lead you along. Just keep looking for the indication of current flowing, when you no longer get that, the short to ground is behind you.

Please keep us informed what you find or don't. Everything matters.

Matt
Matt & Mary Colie
A sailor, his bride and their black dogs (one dear dog is waiting for us at the bridge) going to see some dry places that have Geocaches in a coach made the year we married.

Flute_Man
Explorer
Explorer
Was there any incident just prior to it not working?
Jerry Parr
Jerry Parr
05 Mandalay 40B
Cat C7 350
04 Honda CR-V
Ham Radio K7OU
Retired EE
Jrparr32@gmail.com
602-321-8141
Full-timer