I rebuilt my engine and reinstalled it and when i connected the battery, my main fuse instantly blows making me think there is a short, I looked at the wiring diagram and still can't figure out what might be the cause, I'm currently redoing the grounds.

 

This belongs in the New Member RX-7 Technical Section, and will be moved accordingly. Please keep that in mind. As for the Main Fuse blowing on powerup, this is a dead short, plain and simple. It would be on the side opposite of the battery, do you see any damaged wiring? Since the Main Fuse also feeds several other fuses, it would NOT be on the circuits those other fuses operate as a lower-rated fuse would blow before a larger one will. It will be a game of "one of these things is not like the others", and the alternator can be ruled out since it is on the Battery side of the fuse box.

Realistically, the source of this problem will be under the hood, and probably close to the fuse box. I'd suggest taking a look at the Power Distribution of the wiring diagrams. Look for what the Main Fuse feeds, but Is NOT tied into another fuse.

 

thread moved. please post in the correct sections.

 

I did as you said and I believe I found the issue, my ecu ground was on the battery terminal of the alternator