I have a 96 GMC Sierra W/T. Recently my Sony H/U died (could insert and eject CD's - just no sound, or power on the faceplate). Bought a new Alpine H/U, installed it with the same deal - no power at all, in fact I cant even insert a CD. I used a test light and I'm getting power at the H/U fuse, the yellow 12v battery wire but nothing from the red 12 v ignition wire. I found a blown fuse for the Horn (horn worked before - but I changed the fuse anyway). All other fuses seem to be working.
Not sure what to do? I have an amp and a 12" sub, sitting there, not even hooked up yet - so they are definitely not the cause.
Any suggestions? The ground is definitely working from the Head Unit.... I even ran a ground line from the battery to the head unit - still nothing.
Check under your hood, I know wierd place to look, but I have a 00 blazer and I had a similar problem, there was a Yellow clip looking thing , it had 2 fuses in it, one was blown. replaced it and everything came alive again I don't know how similar these vehicles are but I know gm likes to keep practical!!
Turns out the Radio fuse was blown. Go figure. My buddy spent 5 hours, I spent another 3 hours - and we couldn't figure it out. What got me was the test light. I hit it with the probe, and it lit, but when I hit the other (diode?) there was nothing. Changed it and now the radio works!
It's only a 10A, so if it starts blowing frequently, I'll stick a 30a in...
For each fuse in your fuse panel there is an input side and an output side, you were obviously sticking your testlight into the input side which will continue to show voltage there, but if you put the testlight on the output side you would have got nothing since the fuse was blown and couldn't pass voltage to the output side. It's always best to pull the fuses out to check them if you suspect one is blown.
Also, the fuses are rated at certain amperages for a reason...it is not a good idea to put larger than rated fuses in place of a smaller one....you are asking for trouble that way...at the least, possibly some melted wires, at worst an electrical fire.