My Fiero will not start at all not even crank can someone help me?

Tom is right...principally the BLACK cable that attaches to the chassis ground...get a coarse wirebrush (borrow hal's barbeque brush) brush the end of the black cable what attaches to ground...wirebrush the ground spot...put them together for refreshed ground to the ignition system and fuel pump etc,...however there is another 1/0 battery cable for the starter's requirements..this one attaches to the block near the alternator~ clean that one too if is still not starting~

you did not "reverse jump" ? this would be murder for the Electrical system..we won't go there if you did not induce this violation~

I didn't reverse jump I tried everything for it. Once this happened I let it sit for a few days tried it again and all electrical was back until I turned the key to crank it over then everything went out again and nothing happens now when I turn the key not even the brake light turns on when I hit the brake neither the dome light either

Thank you guys

My fiero won’t start it’s not getting fuel or spark I replaced the battery and replaced the key but all the electrical works