Need help tracking down wiring problem.
 

I swapped in my new 408 about a month ago and got everything bolted down and plugged in, and I tried to load the new tune (previous you've was procharged 6.0) and it won't let me load the tune, BUT it does let me read the old one. So its communicating with the pcm but just won't write. I've gone through and checked several pins and grounds for voltages and everything is good except one. Pin 19 on the blue connector which is key on voltage isn't getting any voltage when the key is on. Pin 19 comes from ECM1 10amp fuse but I can't find that fuse. On schematics it says underhood fuse block bottom. But I can't find a 10amp that is labeled ecm1.

Secondly, my fuel pumps aren't priming when the key is on and 80% of the time my fuel gauge will read empty with the light on, then other times its a little under half a tank which is correct. I believe these problems are related. But is the not loading tune issue related to this as well? Any help is appreciated, thanks.

Check that one wire,, dont look for a 10 Amp fuse it could have been changed to something else.

use your meter and check continuity from that wire to a fuse.

Good point, I will try that thanks