2006 Ford F-150 won’t start!

(Disclaimer: I don’t know much about vehicles and I need
some good advice!) I’ve had a couple issues with my
truck, starting with blowing a head gasket due to a
coolant leak. I opted to have the engine replaced and took
out a loan to do so. Cheaper than buying a new car, when
I still owe a little on this one. The engine is put in,
everything is running great except one lifter isn’t pumping.
The mechanics who replaced it said to drive it for 500,
then bring it back. I did, the problem wasn’t resolved.
Drive it another 1,000. Problem persists, I take it back
around 3,000 miles driven because I’m concerned the
lifter not working properly could cause more damage and
possibly void my warranty on the engine. The head
mechanic of the shop says he’ll replace the lifter, but
keeps telling me he doesn’t know how he’s going to pay
his guy for the labor to do so. (It’s not my problem if the
engine repair is under warranty through AutoZone, am I
correct?) Either way, I left my vehicle with them all day,
and they didn’t replace it. They did, however, plug in an
EGR plug that hasn’t been connected since the
replacement. The other mechanics around looking at the
truck said what a shitty job the original guy did and that
he rushed through and didn’t do proper checks. One of
them takes the truck for a loop and seems to be driving
ok. I take off, thinking everything is good and I’ll get my
part replaced later. I get 15 minutes down the road and all
of a sudden, my engine loses power, the RPMs are
floating between 250-500, bouncing like crazy. I give it a
little gas, and nothing changes, so I pull over. I’m afraid
my truck has overheated again. I let it sit for a few minutes
on the side of the road and try to restart it. It’s clicking like
it’s trying to turn, but it never fires. I have it towed back to
the shop, and they blame the ignition interlock I have in
the vehicle. I’ve had it almost a year, with no problems,
and before the engine was replaced. However, just near
the EGR, there was a melted wire. I didn’t catch exactly
what it was called, or what it went to because they
replaced it/spliced a new wire in before I knew anything
about it, and showed me after the fact. The truck still
doesn’t start. They replace the coil pack, then the cam
sensor, and still nothing. They’re convinced it’s the
interlock causing the issue, saying it shorted out the
“brain” of my truck. I’m guessing that’s the ECU?
However, the device still works, has power, etc. is it
possible the mechanics caused the wire to melt by
moving it when the plugged in the EGR? Could that have
caused the ECU to short and the engine to not fire? I need
help!!! The photo attached is what wire I think was
replaced by them without me knowing until afterwards.