Ok so what I need to know is how I can try to fix it. I checked all fuses in panel also.
I can help you try to fix it, but don't know your electronics skill level. If nothing jumps out at you once you have the radio or amp open, then you'll need a multimeter and the ability to read diagrams and possibly component datasheets. I can assist with that but I can't solder it from here (lol) so odds are you'll need a soldering iron too. Before getting ahead of myself, I'd also make sure the radio has both of the 12V power inputs live. One is for the clock/memory/?? and the other for the majority of the radio power.
First you should get the wiring diagrams linked in my sig, and look through them to see if any of those seem to match your radio setup. Once we're on the same page with the diagram, I can suggest specific things to check with a multimeter.
Next you'd use a multimeter on low voltage AC to detect where the audio signal is lost. For example is it coming out of the head unit to an amp (if present) or not? If there is no separate amp, just for the heck of it I'd still check for signal on one of speaker wire pairs.
You determine if it's the head unit or the amp, then open it, power it up, hook an antenna up so it can tune a station, and follow the power rails and the audio signal chain to find where the fault lies. If it was just one channel out, I'd have guessed a blow output transistor, though the transistor(s) might be integrated into an amp IC, and a severe enough failure could have potentially taken out the whole IC. If you open it and find a big scorch mark on one, you could make the leap to assume that's your problem and not bother with powering it or the antenna. If you're in a strong signal area, a metal coathanger might work instead of fishing the antenna wire out to use it. If it's the amp that's the problem, you'll need to hook the radio up to it or an alternative audio line-out signal level to troubleshoot it. Without knowing any differently, a target for input signal level would be around 1VAC, and could be anything really, even the headphone out from a cellphone through a cable cannibalized off a pair of $1 earbuds if you have nothing else, or RCA cables from the aux out on a home stereo, etc. .
It is doubtful that Ford used something proprietary so you would note the IC pin count and functions on the respective datasheet to pick a functional equivalent if that exact IC is no longer available, or if there are no known good sources. Try to avoid sellers on ebay shipping from China, as they are often selling counterfeits of something that old, some cheap low power chip stuffed into a larger package.
I'm going off on a tangent since it might not be the amp IC. Good (well lit, high resolution) pictures inside the suspect radio or amp might help, but you'll need to post them on a hosting site like imgur.com then link them here because the image size limitations here are far too small for seeing detail on circuit boards.
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