Stereo Wiring Problems in 93 Sable

My car stereo wont start, i checked all the speaker wires, nothing is touching metal, i also had my stereo brought in to be fixed and no problems were found. So, a friend of my dads suggested that the ground coming from the back of the stereo could be loose (he is very knowledgeable with cars). I have a 1993 Mercury Sable with the 3.0L v6, where can i find where that ground is hooked up to, it looks like it goes a way in, i cannot see it from the empty stereo spot, am i going to have to remove parts of the dash or is there somewhere i can find it by looking under the dash? Any help would be great, thx.

i redid my 93 stereo. did you hard wire it or did you buy a converter? also did the old head unit work when you took it out if so you wired it wrong. i can give you wiring code when i take my beloved car apart tomorrow. i bought a new car after 182 thousand miles, so i will be tearing it out tomorrow i can get you the wiring diagram tomorrow if i think of it. you probably just wired it wrong.... do you know anything about what you were doing? because they deliberately make it so that people who either are not certified to work on those stereos from ford and mercury or know exactly what you are doing. if you know what you are doing you can simply find out which wire is which with your trusty little voltage meter. let me know. good luck