What one is the live wire for the radio for

Did you bridge the new stereo into the truck using the factory original radio circuit or from another live connection? Does the new stereo have a permanent power wire and where is it hooked up to? Is the battery flat? Trace the wiring mod you have done back to the fuse block and ensure you have left all the factory connections working. Check your fuses and relays so you haven't accidentally grounded a live circuit and damaged something. Best way to go is using an adapter harness like this -
86 93 Select Mazda Ford Mercury Radio Harness to Aftermarket Stereo...

12 volt constant wire for the memory must be working
should keep the clock working and pre sets

12 volt wire from ignition acc is not giving 12 volts to radio

may have an inline fuse or check radio fuse
internal fuse cover has a legend

using on /off buttons might mean
resetting stations and stuff every time you want to drive

radio has to be factory radio because factory radio is programmed to vechicle PCM and theft security system any kind radio wont work with your vechicle has to be factory model radio has to be reprogram.

more than likely you have blown a fuse. check fuses first and check back. ususally the courtesy light and radio are on same fuse. Next time remove ground from battery before installing any electrical equipment...trust me...it just saves a lot of aggro and money

Hi there:
Check this on 2005 Chevrolet Trailblazer Car Stereo Wiring Chart...

Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: The radio harness does not provide a switched power source. Run a wire to the fusebox for switched power.
Car Radio Ground Wire: Black/White
Car Radio Illumination Wire: N/A
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

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

Do these colors match your truck wire colors? Let me know if not or if you have more questions.

1991 Ford Ranger Pickup Truck Car Radio Stereo Wiring Diagram
Car Radio Battery Constant 12v+ Wire: Green/Yellow
Car Radio Accessory Switched 12v+ Wire: Yellow/Black
Car Radio Ground Wire: Chassis
Car Radio Illumination Wire: Blue/Red
Car Stereo Dimmer Wire: N/A
Car Stereo Antenna Trigger: 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 (+): Orange/Green
Left Front Speaker Negative Wire (-): Black/White
Right Front Speaker Positive Wire (+): White/Green
Right Front Speaker Negative Wire (-): Black/White
Car Audio Rear Speakers Size: N/A
Car Audio Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Pink/Green
Left Rear Speaker Negative Wire (-): Pink/Blue
Right Rear Speaker Positive Wire (+): Pink/Blue
Right Rear Speaker Negative Wire (-): Green/Orange

Car Radio Constant 12v+ Wire: Orange
Car Radio Switched 12v+ Wire: Ignition Switch (The radio harness does not provide a switched power source. Run a wire from the Ignition Switch.)
Car Radio Ground Wire: Black
Car Radio Illumination Wire: Gray
Car Stereo Dimmer Wire: N/A
Car Stereo Antenna Trigger: Pink
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: N/A
Front Speakers Size: N/A
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
Rear Speakers Size: N/A
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
Good luck and hope this helps.

It sounds like a wire somewhere in the wires that run to the speakers is getting a short. Something very similar happened on my mothers car. I trouble shot it and eventually found out it was the stereo that needed replacing.
You can buy a new stereo anywhere that sells them. Be cautious of used as you never really know what you are getting. Installing a new stereo is not very difficult but you have to make sure you have everything you need. You can get everything you need at your local electronics store. Just go to the mobil audio section and tell them which stereo you want and that you need the stuff to install it. All the places around where I live have free instalation with the purchase of a new stereo. Most after market stereos will require a dash kit to fill in the space left over from the size difference between the factory stereo and the after market stereo.

• First thing to do is isolate all the cables from each other and put insulating tape over the bare cables.
  
• Now using a multimeter set on 12 volts or above test each cable in turn with the ignition on.
  
• You will find one live cable that is only live when you have your ignition in the number one position.
  
• This is the live feed to your radio, fit a small amp-age fuse (5 or 7.5 amp) depending on the rating for your new radio.
  
• You will have speaker wires, these you can identify by tracing them from each speaker.
  
• By now you will have identified your live cable and your speaker cables.
  
• You may have a secondary live for a electric aerial and an earth cable. You must earth your radio even if you have to make an earth on the inner bodywork.
• If you do not need the secondary live then make if safe.
  
• If you need the secondary live fit an appropriate fuse.
• Earth the new radio.

I use this system on used cars before fitting radios/cd players. It works but be careful.

Memory wire on new radio needs a live connection ie source that is live with ignition switched off.