Noise Kill Circuit Confusion

[The Chief]

Hey guys, I need help. I have searched and searched in an effort to figure this out on my own buy my last resort is to ask for help so here's my first post.

I have a 2001 International/Amtran bus. We use it for tailgating and staying warm between hockey games for our kids. Recently, the entire noise kill circuit started blowing a fuse killing all of the fans which completely defeats the purpose of the bus.

I have replaced the solenoid/contactor that controls the noise kill circuit. I have identified almost all of the fuses in the fuse block and matched them back to the diagram on the inside of the door. The fuse that keeps blowing is a 10 amp fuse that I can only identify as "Spare" on the diagram. The fuse blows when the noise kill circuit is on and when it's off. To this point, it only blows when the bus is in motion which leads me to believe there is a wiring bouncing around somewhere grounding out, blowing the fuse.

I have recently replaced the flashing lights with LED's and thought maybe one of the wires I unplugged was shorting out. I have since taped off every loose wire and removed the controller that handled the flashing lights.

I traced the little gray wire from the contactor and it goes straight to the switch at the helm, doesn't go through the fuse block to the "spare" fuse or anything.

I'm at a loss here. What could I have changed on that circuit that is blowing an obviously not "spare" fuse.

Please let me know if anyone else has experienced this and what you found to be the issue. If you need pics or further info, please let me know how I can help you, help me!

Thanks all,
Jeff

 

[Timeline]

A bad fan motor?

 

[ewo1]

What generally "pops/blows" a fuse is either a dead "+" short to ground or overheating of a wire/circuit.

If the fuse pops "immediately" it is a short to ground.

If it blows/pops slowly then it probably a failing component or wires maybe melting/fusing together...

Post #8 in THIS THREAD, you'll find wiring diagrams that might help....

More diagrams in THIS THREAD too...

 

[The Chief]

A bad fan motor?

All fans have their own fuses. I'd guess if it was a bad fan motor, it would blow its individual fuse.

 

[The Chief]

What generally "pops/blows" a fuse is either a dead "+" short to ground or overheating of a wire/circuit.

If the fuse pops "immediately" it is a short to ground.

If it blows/pops slowly then it probably a failing component or wires maybe melting/fusing together...

Post #8 in THIS THREAD, you'll find wiring diagrams that might help....

More diagrams in THIS THREAD too...

These are great! I actually found these a year or so ago when I was researching which bus to buy. I couldn't remember what bus type they were for or find them again. I'll start researching now, thanks!

 

[ewo1]

Hey, I took a look at all the diagrams I uploaded in those two posts and could not find a "Noise" circuit.

I did some deeper digging and found this diagram.
It covers IC busses manufactured after March 01, 2000.

It comes from the service manual S08286.

Here is a link to the complete diagram. You want to look at page 42.

http://bodybuilder.navistar.com/General/Documents/svcmanpdf/S08286a.pdf

 

[The Chief]

Hey, I took a look at all the diagrams I uploaded in those two posts and could not find a "Noise" circuit.

I did some deeper digging and found this diagram.
It covers IC busses manufactured after March 01, 2000.

It comes from the service manual S08286.

Here is a link to the complete diagram. You want to look at page 42.

http://bodybuilder.navistar.com/General/Documents/svcmanpdf/S08286a.pdf

Ahhh....here we go. I was looking through the first set of links last night, and, while similar, none of the fuse blocks were the same. This is the same as what I'm working with. I'll get out to the barn this weekend with my laptop and do some more wire chasing.

Thank you so much for the information and your time spent digging it up. I greatly appreciate it.

I remember now, I came across the bulk of your links when I was researching transmissions. I too have the 3060 and I was able to get 6th gear unlocked. All thanks to the fine folks on this forum.

 

[nikitis]

Another thing to maybe consider is that some item on the line is faulty and drawing too much wattage. I experienced a similar issue when a Chinese company sent me 120V LEDs vs 12v LEDs. I wires in the 120V thinking they were 12V and fuse would pop instantly. As a test I would try a 20 amp fuse and see if it holds. If it does hold you could just be slightly over volted even if mathematically in your head it doesn't make sense.

Be sure you can watch the line though because in the 20amp range the wiring if too thin could melt and burn instead of the fuse.


If it still pops at 20 amps then something is definitely still shorting somewhere.

You may want to physically trace the line from front to back and for every item it connects to, add up the amps required for those devices. If a single light is 12v 2amp, that's 24 watts, if two lights it is 12v 4 amps because 2amp +2amp =4amps for two lights on the line. Add up the amps total for all devices on that line and then make sure it's under the fuse size you use. You also have to take into account the wire gauge size as they are rated to only handle a certain amount of amps, and if your fuse is bigger than your wires, the popping will occur on the wires themselves rather than the fuse. Wires pop at their weakest link. Think like a frayed rope, it's weaker where it is frayed. Wires and amps are the same and the fuse by design is a controlled frayed spot meant to be weaker than the wires, this is why we don't put higher sized fuses when lower ones pop usually.

Whenever you run into an electrical issue of this nature, go and physically inspect all devices and add up the total amperage from each device and do the math. If you are under spec then it is definitely a short somewhere then.

 

[The Chief]

I got some time in the barn last night and found that not all buses are wired equally. Using the diagrams provided (thank you ewo1) I traced the 10 amp circuit and even though the diagram on the bus shows it as a spare, it actually matches the provided diagram and I found it going to a busbar. The magic here is that it was jumped to other circuits. These circuits could be ones that I removed (warning lights, crossing gate, stop sign, door buzzers, etc) and maybe had a loose, exposed, wire bouncing around.

Long story short, I removed the jumper making the noise kill contactor the ONLY thing on that 10 amp fuse. I tested the functions of everything I need on the bus and everything is operational. Once the snow melts, I'll take it for a spin and confirm that I have finally fixed my problem.

Thanks for all of the info and input.