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Author Topic: Weird Electrical problem  (Read 882 times)
puff501
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« on: November 06, 2017, 12:06:01 PM »

We have a 94 MCI 11.  Start the bus and the running lights go on with all the switches in the off position.  Brake lights are also on.  It seems once the bus airs up, the lights go off, however the brake lights no longer work.  Also when you put on the headlights only on, the headlights come on as well as all the running lights and the brake lights.  Also the fast idle will not work unless you put on the headlights or the running lights.  While it is idling with no lights on, intermittently the running lights as well as the brake lights wil come on, stay on for a minute or so, and then go off.  It will do this, seemingly randomly, while it is sitting there idling.
There is some weird stuff going on here.  It's got me scratching my head.  I spent about an hour trying to figure this out and haven't dove into it yet checking wires and stuff.
Just wondering if anyone out here ever experienced anything like this.
Steve
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bobofthenorth
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« Reply #1 on: November 06, 2017, 12:25:20 PM »

In this specific case I have no insight but my experience has been that when you have weird electrical $#!% happening its always the ground.  Can't help you with where but I'd focus on the ground(s).
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« Reply #2 on: November 06, 2017, 01:11:07 PM »

I don't know much about big buses but I did notice that the brake lights on my '90 MCI 9 came on at start up and stayed on until the air pressure was up.  Jack
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Dave5Cs
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« Reply #3 on: November 06, 2017, 01:34:04 PM »

We have a 94 MCI 11.  Start the bus and the running lights go on with all the switches in the off position.  Brake lights are also on.  It seems once the bus airs up, the lights go off, however the brake lights no longer work.  Also when you put on the headlights only on, the headlights come on as well as all the running lights and the brake lights.  Also the fast idle will not work unless you put on the headlights or the running lights.  While it is idling with no lights on, intermittently the running lights as well as the brake lights wil come on, stay on for a minute or so, and then go off.  It will do this, seemingly randomly, while it is sitting there idling.
There is some weird stuff going on here.  It's got me scratching my head.  I spent about an hour trying to figure this out and haven't dove into it yet checking wires and stuff.
Just wondering if anyone out here ever experienced anything like this.
Steve

Hi Steve MCI never made an MC11, it would be a 9 or a 12. That being said My 5C is the same as Jack was saying and when I turn on the headlights the clearance lights also come on. I have a separate clearance light switch also if I just want to turn them off as in the day time and just run my headlights. As far as anything coming on Intermittently that is as Bob said nothing but a loose or bad ground. Look in your manual and there is an electrical section which will tell you where the instrument panel or side switch ground is located. Should be in the drivers outside panel electrical box. Before playing in there make sure you turn your battery switch off as well as unplug the coach and house batteries turned off just in case.
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« Reply #4 on: November 07, 2017, 03:05:12 AM »

Unless someone has messed with it...

By design,

The headlight switch will turn on all the exterior clearance/tail and headlights.
The Clearance switch will just turn on the clearance/tail lighting.

The brake lights are activated by both the brake pedal and the parking brake.

Parking brake applied, the brake lights are on.

x2 what bobofthenorth said. Grounds, grounds grounds.

The wiring in both the driver's side switch panel, and the dashboard is all exposed connections, surrounded by the metal framework. You WILL short against the framework, if you try removal or replacement with the batteries engaged.

Carefully get the switch panel out, religiously ensure all is set there in a giant spaghetti mess not touching, then put the power back on for trouble shooting.

Use the schematic out of the maintenance manual, and trace the wires from switch to the junction studs in the panel outside under the driver's window, to do a bit of confirming that "modifications" have not been made. You MUST NOT trust what is in there. You regard the previous owners as having completely #$%^#$ the wiring up, until proven innocent.

Busnuts inherit BIG problems from previous owners. Dangerous, fire causing problems, not just inconveniences like you describe.

be safe, be patient, prove out your circuits, check the grounds.

happy coaching!
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« Reply #5 on: November 07, 2017, 06:37:48 AM »

I think what you have is a 102C3 or 102A3.  I would think that you have a short in the lighting system and when the circuit breaker opens the lights go off.  When it cools they come back on.
Jack
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puff501
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« Reply #6 on: November 07, 2017, 08:10:31 AM »

Ok, I thought I had a MCI 12, fat fingers, but anyway it's an old Greyhound bus, converted to haul inmates.  And yeah I've been in that compartment under the drivers window before, wires and relays all over the place, it's a mess.  Many people have been in there before me.  There is one 12 volt stud that has about 10 wires attached to it where everything that is 12 volt in the bus is hooked to. 
What Jack says, it seems the relay heating up and cooling off and engaging and disengaging is logical.
I'll also pull that switch panel too and check the connections and look at grounds too.  And yeah power off when messing in that switch panel, It's a freaking mess in there.
Probably dive into it today.
Thanks all, here we go!
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« Reply #7 on: November 07, 2017, 08:57:10 AM »

Steve what you have is probably an MC12. (which is technically a refurbished MC9)
And I agree you have a bad ground short or possibly a weak breaker.
Back in the day when I worked on a fleet of MCI's (and other peoples too) I often found where Greyhound mechanics had by passed both switches and hard wire the running lights to where they came on automatically when the ignition swith was turned on.
But even then I experienced problems with shorts and BAD GROUNDS.
Grin  BK  Grin
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« Reply #8 on: November 07, 2017, 12:27:44 PM »

Get someone else to turn things on, be by the outside door and you should hear the breaker pop.  If you can't feel and see if you can find one with heat to the feel.  A lot of the MC 12 have a series 50 engine, which one do you have.
Jack
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« Reply #9 on: November 07, 2017, 12:37:50 PM »

Get an IR gun (cheap these days) and read temp of each circuit breaker. Look for warmer one. Same for all bolted connections. If it is just a bad or weak circuit breaker, get one of the same rating and connect jumperwires to it. Parallel original to check it. Don't try to just use a unfused wire to bypass unless you want smoke and burned wires.
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« Reply #10 on: November 08, 2017, 06:32:24 AM »

Hi Steve,

Go into the drivers electrical compartment outside your bus. Look on the very bottom you will see a series of ground blocks.

Pull on them back in fourth. Look for corrosion at the base.. Very common for them to corrode and give you problems like you describe!

Nick-
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« Reply #11 on: November 08, 2017, 12:59:02 PM »

It is definitely usually the ground.

Having said that - if your bus is setup to have the brakelights on until air pressure is built up, and then be controlled by the braking action, then possibly your brake switch is broken?

Or do the brakes "work" in the sense that while airing up you can make them come on and off by pressing the brake pedal?
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« Reply #12 on: November 08, 2017, 05:20:14 PM »

like Nick said       I had to add a larger wire to a new ground for both the blocks as the blocks had bad ground connections 

dave
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« Reply #13 on: November 08, 2017, 06:34:46 PM »

I read Nick's post and decided to go check out the bottom of my drivers side electrical compartment and I found the connectors to be corroded, so I will figure out how to deal with that.  But then I noticed a whole bunch of wires that look like they used to be connected to one of these blocks but were taken off at some point (I've attached a picture of the wires in question). 

I wasn't able to follow the wires, they appear to go into a large wire harness heading up front.  Any thoughts on leaving them as-is vs re-attaching them to one of the blocks?  Since I have no idea what they go to I think i should leave it as-is but interested in hearing your guys opinion.
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eagle19952
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« Reply #14 on: November 08, 2017, 06:39:34 PM »

those would definitely be leverB wires in my opinion Smiley
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« Reply #15 on: November 08, 2017, 06:49:31 PM »

those would definitely be leverB wires in my opinion Smiley

Thanks eagle, I assume by leverB wires your mean leave those freaking wires alone?
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eagle19952
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« Reply #16 on: November 08, 2017, 06:59:43 PM »

Thanks eagle, I assume by leverB wires your mean leave those freaking wires alone?
yup, until you know what and where leave them as is..maybe tape them up.
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« Reply #17 on: November 08, 2017, 07:30:11 PM »

yup, until you know what and where leave them as is..maybe tape them up.


Thanks brother, I appreciate it!!!
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