My rear speakers are humming and i've changed the cd player and the same thing

The humming sound prior to cutting out could indicate a short in the unit itself.....remove unit and have it tested!

Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: Yellow
Car Radio Ground Wire: Black
Car Radio Illumination Wire: Gray
Car Stereo Dimmer Wire: N/A
Car Stereo Antenna Trigger Wire: N/A
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Car Audio Front Speakers Size: N/A
Car Audio Front Speakers Location: N/A
Left Front Speaker Positive Wire (+): Tan
Left Front Speaker Negative Wire (-): Gray
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Dark Green
Car Audio Rear Speakers Size: N/A
Car Audio Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Brown
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Dark Blue
Right Rear Speaker Negative Wire (-): Light Blue

Not sure I understand your question. Did you buy a harness adapter for GMC, or are you trying to just cut the connector off the factory radio and solder it to your CD player? If the latter, below is the color code for your factory wiring.

1994 GMC Sierra C1500 Car Radio Wiring Schematic
Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: Yellow
Car Radio Ground Wire: Black/White
Car Radio Illumination Wire: Brown
Car Stereo Dimmer Wire: Gray
Car Stereo Antenna Trigger Wire: N/A
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Car Audio Front Speakers Size: N/A
Car Audio Front Speakers Location: N/A
Left Front Speaker Positive Wire (+): Tan
Left Front Speaker Negative Wire (-): Gray
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Dark Green
Car Audio Rear Speakers Size: N/A
Car Audio Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Brown
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Dark Blue
Right Rear Speaker Negative Wire (-): Light Blue

Yellow wire on cd player is for memory and needs to be on constant voltage that doesn't shut off when car is turned off.

Here is the wiring diagram for the car:

Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: Yellow
Car Radio Ground Wire: Black
Car Radio Illumination Wire: Gray
Car Stereo Dimmer Wire: Brown
Car Stereo Antenna Trigger Wire: Pink
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Car Audio Front Speakers Size: 5 1/4′
Car Audio Front Speakers Location: Doors
Left Front Speaker Positive Wire (+): Tan
Left Front Speaker Negative Wire (-): Gray
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Dark Green
Car Audio Rear Speakers Size: 6′ x 9′
Car Audio Rear Speakers Location: Rear Deck
Left Rear Speaker Positive Wire (+): Brown
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Dark Blue
Right Rear Speaker Negative Wire (-): Light Blue

DOES THE RADIO PLAY? HERE ARE THE FACTORY WIRING COLORS FOR THE RADIO HARNESS, RECHECK YOUR WORK. IF U FIND NOTHING THEN IF THE RADIO PLAYS THE CD PLAYER IS DEFECTIVE, IT HAPPENS BELIEVE ME.

2001 Chrysler 300M Car Stereo Wiring Diagram
Car Radio Battery Constant 12v+ Wire: Pink
Car Radio Accessory Switched 12v+ Wire: Red/White
Car Radio Ground Wire: Chassis or Strap
Car Radio Illumination Wire: N/A
Car Stereo Dimmer Wire: Orange
Car Stereo Antenna Trigger Wire: Orange/Red
Car Stereo Cell Phone Mute Wire: N/A
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: Located under the rear deck in the trunk.
Car Audio Front Speakers Size: N/A
Car Audio Front Speakers Location: N/A
Left Front Speaker Positive Wire (+): Dark Green
Left Front Speaker Negative Wire (-): Brown/Red
Right Front Speaker Positive Wire (+): Violet
Right Front Speaker Negative Wire (-): Dark Blue/Red
Car Audio Rear Speakers Size: N/A
Car Audio Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Brown/Yellow
Left Rear Speaker Negative Wire (-): Brown/Light Blue
Right Rear Speaker Positive Wire (+): Dark Blue/White
Right Rear Speaker Negative Wire (-): Dark Blue/Orange

1992 Saturn SL2 Car Stereo Radio Wiring Diagram
Car Radio Constant 12V+ Wire: Orange
Car Radio Ignition Switched 12V+ Wire: Yellow
Car Radio Ground Wire: Black
Car Stereo Illumination Wire: Gray
Car Stereo Dimmer Wire: Brown
Car Stereo Antenna Trigger Wire: N/A
Car Stereo Amplifier Trigger Wire: N/A
Front Speakers Size: 6 1/2′
Front Speakers Location: Doors
Left Front Speaker Wire (+): Tan
Left Front Speaker Wire (-): Gray
Right Front Speaker Wire (+): Light Green
Right Front Speaker Wire (-): Dark Green
Rear Speakers Size: 6 1/2′
Rear Speakers Location: Rear Deck
Left Rear Speaker Wire (+): Brown
Left Rear Speaker Wire (-): Yellow
Right Rear Speaker Wire (+): Dark Blue
Right Rear Speaker Wire (-): Light Blue

here are the factory wire colors and what they do.

1999 Ford Escort
Radio Stereo Audio Wiring Diagram
Car Radio Battery Constant 12v+ Wire: Blue/Red
Car Radio Accessory Switched 12v+ Wire: Blue/Black
Car Radio Ground Wire: Black
Car Radio Illumination Wire: Red/Black
Car Stereo Dimmer Wire: Green
Car Stereo Antenna Trigger: N/A
Car Stereo Amp Trigger Wire: White/Orange
Car Stereo Amplifier Location: Under the driver seat.
Car Audio Front Speakers Size: N/A
Car Audio Front Speakers Location: N/A
Left Front Speaker Positive Wire (+): Violet
Left Front Speaker Negative Wire (-): Blue/Orange
Right Front Speaker Positive Wire (+): Blue/White
Right Front Speaker Negative Wire (-): White
Car Audio Rear Speakers Size: N/A
Car Audio Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): White/Blue
Left Rear Speaker Negative Wire (-): Red/Blue
Right Rear Speaker Positive Wire (+): White/Green
Right Rear Speaker Negative Wire (-): Blue
-->

I think that it may have a ground that is heating up, if the aftermarket cd player is grounded to a painted bolt this is what happens.

HERE YOU GO ALL WIRES U NEED PLEASE RATE ME GOOD LUCK WILL WORK GOOD!!!!!!!!


2003 Ford Focus Car Stereo Radio Wiring Diagram
Radio Constant 12V+ Wire: Orange/Black (Thick Wire)
Radio Switched 12V+ Wire: Yellow/Green
Radio Ground Wire: Black/Yellow and Black/Green
Radio Illumination Wire: Orange/Black (Thin Wire)
Radio Dimmer Wire: N/A
Radio Antenna Trigger Wire: N/A
Radio Amp Trigger Wire: None
Front Speakers Size: N/A
Front Speakers Location: N/A
Left Front Speaker Wire (+): White/Black
Left Front Speaker Wire (-): Gray/Black
Right Front Speaker Wire (+): White/Red
Right Front Speaker Wire (-): Gray/Red
Rear Speakers Size: N/A
Rear Speakers Location: N/A
Left Rear Speaker Wire (+): White/Purple
Left Rear Speaker Wire (-): Gray/White
Right Rear Speaker Wire (+): White
Right Rear Speaker Wire (-): Gray
-->

i supose the am fm radio just dosnt cut it anymore well lets give this a try . first u must disconnect positive battery cable so you dont short any wires . remove screws that hold in factory radio pull radio out a feww inches as no to rip out any wires.next you must locate positive 12 volt power supply wire usually red or orange .if not shure connect battry cable again and use a 12 volt test light by attaching the ground cable on the test light to a good clean metal bracket under dashboard or connect to a black groundwire with a screw into the steel under dash next probe the wires goin into the factory radio ur looking to find power 12 volts once you have found the correct power wire use tape and mark it this will be the power wire for your new stereo next u must figure out what wires for what speakers osually 2 wires per speaker 2 rear speakers and 2 front speakers meaning a total of 8 wires follw me so far ? now disconect car battry again so not to have sparks and cut or disconnect remaining wires speakers first label all with tape and mark front right front left rear left rear right there is a + and - the wire with the stripe on it is usually the + the other wire is the - being negitive ground . this operation is important in order for your fade ballance controlls to work properly now with your new cd player inhand look and see what wire is gonna be 12 volt most times its red with a fuse eg white plastic connector small fuse inside there it a must proper fuse to protect new cd player now there will be a black negative this will go to the matal ground area under dash close to where cd player goes into dash red to the orig taped 12 volt supply now ur spks one pos+ and one neg or common to each speaker now make all conections with stereo before you push stereo into dash you must hook up car battry leaving cd player hanging out so you can make wire changes if you wish on the speakers you need to use one pos front right or rear right + with one common or neg black - to the spkr the same common or ground or - whatever its called one common or neg can be used for all spkrs .good luck tape and solder all connections after you feel all is good im sorry this is all the help i can offer you be careful