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Old 05-03-2015, 11:07 AM   #1
Bus Nut
 
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2000 GMC Microbird Electrical questions

I might be an old mechanic, but I'm new to school bus's.

I just bought a 2000 GMC Micro Bird 19 passenger and it has a couple electrical ... gizmos ... that I don't know the first thing about.

Hopefully, y'all might be able to help me identify some of this stuff. See the pictures below.



The "Merlin" box has a number of lights/buttons on it. they are labelled: CPU - Txd - Rxd - Cor - Ptt

I don't have a key to open the large black box by the door. There are no labels or markings on this one, but, there is a number of wires going into the back of it.
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Old 05-03-2015, 11:10 AM   #2
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That stuff is all not needed.

It should have been removed by the school division before the bus was sold.

I would trace the wires back to the fuse box, and remove it all.

Nat
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Old 05-03-2015, 11:11 AM   #3
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Since I'm new to bus stuff, I would LOVE to get a wire diagram for the GMC chassis AND one for the Bluebird coach body. I am assuming that they are separate.

Any suggestions where I might look for these things?
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Old 05-03-2015, 11:14 AM   #4
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Quote:
Originally Posted by nat_ster View Post
That stuff is all not needed.

It should have been removed by the school division before the bus was sold.

I would trace the wires back to the fuse box, and remove it all.

Nat
Hey Nat,

I was pretty sure I didn't need it and planed to remove it. I'm just curoius to know what this stuff is (was).

Thanks!
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Old 05-03-2015, 11:14 AM   #5
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Quote:
Originally Posted by Tedd View Post
Since I'm new to bus stuff, I would LOVE to get a wire diagram for the GMC chassis AND one for the Bluebird coach body. I am assuming that they are separate.

Any suggestions where I might look for these things?

Good luck.

Most buses wiring will change from bus to bus.

I would just trace the wires back to what ever is in question.

Nat
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Old 05-03-2015, 01:52 PM   #6
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Pic # 1 is probably a video camera. The dark circle in the middle looks like a lens.

Pic # 2 is for a radio data link. I don't know the brand, but it either is a modem to connect to an external 2-way radio, or it is an integrated modem and radio package. I could tell you more if I could see the back connectors.

If you don't want this, I would like to take a look at it. PM me for an address and I will reimburse you UPS or USPS ground shipping. If you don't want the camera, toss that in.

CPU - usually a "heartbeat" LED. It should flash every few seconds to confirm that the internal software has not crashed.

TxD - transmit data - when this lights, the bus is sending out information.

RxD - receive data - when this lights, the bus is detecting another data signal of the same format coming in

Cor - an old term left over from tube-type radios. It means "carrier operated relay." When this lights, it means the radio squelch has opened because the channel is busy. The "carrier" it has detected is not necessarily data (see RxD), it could be a voice transmission or just some interference. The Cor on a modem like this is used to delay a transmission from the bus until the channel is clear.

PTT - "Push-to-talk," a term for exerting a transmit command that is based on using the button on the side of a microphone. When this is lit, the bus transmitter is on the air. The data (TxD) might be delayed after the PTT to be sure the radio and modem on the other end are ready to receive.

Picture #3 is a vault for a video recorder to store the pictures from the daily run. Some districts have less recorders (or cameras) than buses, they rotate them through the buses as a psychological deterrent. The kids (and maybe the driver & monitor) never know which days they are being taped, and which they are not.

You could drill the lock and replace it with your own so you could have a place to store valuables.
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Old 05-03-2015, 02:49 PM   #7
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I found the Merlin on a search. I thought the case looked familiar. It is made by Pyramid, a company that makes boxes that let cops & firefighters operate their mobile radios from their handhelds when out of the vehicle.

The Merlin is one piece of an Automatic Vehicle Location suite of products. The box does not include a radio, but does include a GPS chip that feeds position data to the modem. The Merlin can be programmed to "snitch" the bus's location when connected to a radio in one minute steps between one minute to 4 hours.

It also has 3 status inputs. One could be wired to report when and where each time the passenger door was opened, for example.

The inputs can be combined and wired to a "Mayday" button. One input's function can be programmed to change the location report frequency to steps of 5 seconds instead of one minute during an emergency (bus-jacking?).

You would need external equipment and software to make use of the location information that the unit transmits.
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Old 05-03-2015, 03:27 PM   #8
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Radio Engineering's Bus Watch can also be found online. It's basically like an aircraft Black Box but for buses. A lot of bus companies are installing these now for legal liability or insurance reasons.
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Old 05-03-2015, 07:08 PM   #9
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We throw a ton of these black boxes in the junk pile. I use a few at the shop for tool boxes. They remind me of a ammunition can from the army.

Nat
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Old 05-03-2015, 08:07 PM   #10
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Thanks for all the info Redbear. I appreciate it and I'm sure Tedd and others do as well. Working or not it might serve as a theft deterrent even if not hooked up--but then I'd prefer a claymore hidden just under the beaded seat cover on the drivers seat. Just saying.
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