No power to head unit

I replaced the stock JBL head unit years ago. Many hours on the phone with Crutchfield . Years later, my JVC unit has been working fine until yesterday. No power! I think the JVC is toast not power. I check the fuse under the left dash, it's good. I buy a nice Sony unit from Crutch, installed today, can't turn it on. No Power! WTF? I checked all fuses with any audio or entertainment label. That's under the dash and under the hood. Diagnosing electric is not in my skillset yet.
Do you have suggestions for the problem or where to start looking? Much appreciated.

 

Did you have the new radio bolted in when you checked for operation. That can make a difference on some of these trucks.

 

Are the AC controls plugged in and functioning also? The radio circuit is not complete if the AC controls aren't plugged in.

 

This and many aftermarket head units have a fuse on the rear of the head unit too

 

I have checked the fuse in the new unit. Everything was essentially "plug and play". Besides, I lost power on the long time JVC unit.

 

Have you tested any of the wiring to the head unit for power and ground?

 

Therein lies the rub...I have a multimeter but ...

 

Unplug the main harness from the back of the JVC. There should be a ground, switched 12 and constant 12v line along with aux lines and the 8 speaker leads. Ground is black, constant is Yellow and switched is red. Set your multimeter to DC voltage. With the key on engine off, you should have 12v on that red wire of the stereo harness. If you do, you know you are getting power to the radio. Check the fuse right next to the radios harness as Shifty mentioned. Visual inspection and ohms check using your multimeter.

 

@FJR Which JVC headunit are you rocking?

 

https://youtu.be/5kXvam2VVek

 

But you don't know how to use it? Or just haven't busted it out yet? It's really your key to testing whether you've got power is getting through the fuse in the fusebox.

Question: How did you connect the wires? Did you do the ignorant newbie thing and use wire nuts and/or electical tape, or did you do things correctly with crimped connections /or/ solder & heat shrink? If you didn't do one of the latter two, you need to stop what you're doing, unhook everything, and properly terminate/connect your wiring using butt splices or similar terminators, unless you're masochistic and love soldering.

If you did the newbie thing and connected things like my 10yo likes to do, there's a strong chance either (A) a wire has separated OR (B) a wire separated and arc'd to pop a fuse. Sometimes fuse blows aren't obvious, and they don't always blow at the interior fuse box.

I suggest using that multimeter checking continuity on the radio fuse - both the one on the back of the head unit AND the one in the dash fusebox, since sometimes it's not visually obvious the a fuse has blown, many times I've failed to notice the break, until I shine a light from behind.

And make sure you're checking the correct fuse, also, since the labels being under/over the actual fuse may confuse you into thinking you've got the correct fuse when it's actually the fuse above/below it.

Another thing you can potentially do to verify the radio, if you have a 9v battery, you can try wrapping the black ground wire around the negative terminal of the 9v, then twisting together the yellow and red wire in the harness, touch those to the positive terminal of the 9v; you should at least have the head unit light up; if not, the HU is fried.