electrical troubles

[yukon724]

How's it going? new to this site and just like everyone here, i enjoy working on GM Trucks. i made the mistake of buying a 93 2dr Yukon sle that has nothing but electrical issues. mostly focusing on the engine compartment. these wires are no longer made, and honestly for 6 months now i have been going from junkyard to junkyard in hopes of tracking these wires. this is my first SUV project so any advise or info would truly help.

Back to the issue at hand, i found 4x2 engine wires to put in temporarily, at least to get this thing started, however i now have a code 54 and 15. i have checked the wires for cuts, replaced the fuel relay on firewall, tested the fuel pump and i am getting spark. My next move is replacing the ECU. Any ideas to what else could possibly causing the issue?

By the way i cant even compare my truck to these insane classics, they are incredibly difficult to find. hopefully sometime next year, my next project will consist of a 50 GMC pickup. Thanks for your time and help everyone.