If you can, start with a known working console that has little to no corrosion!!!!
Look at the battery terminals and cart connector pins, if there’s corrosion there it’s likely the inside is corroded too, not good!
It’s recommended you find another console to mod…
Test for power, sound, and game properly booting.
However!!!
This mod does not require a completely working GBA!
Bad LCD: if you hear sound but nothing on the LCD you may still be able to use the GBA for the mod.
It’s also possible the power switch is so corroded it will not power on, try working it back and forth a lot, if it shows signs of life try the bypass mod shown in the Disassemble and Prep page linked below.
Same with sound, if there’s no sound work the wheel back and forth a bunch, listen for anything, even no sound does not mean it won’t work, try the bypass mod and retest!
I find video explanation of the installation is best:
Rev 1 of full case with Kynar breakout board: Voultar
Rev 2 of full case with Kynar breakout board: Dubesinhower
Rev 3 of the case with custom CPUflex panel: Macho Nacho Productions
Below are older write ups for Rev 2 of the full case and LCD version of the kit:
