Does too much alcohol applied when cleaning a cartridge damage it

99% isopropyl alcohol should not damage the cartridge if you are using it to clean the contacts. If you get the alcohol on the cartridge’s label, it may remove the ink, or start to loosen up the glue that holds it on.

Alcohol is not electrically conductive, and I have seen people spray it on running devices to try to track down shorts since shorted components get hot and cause the alcohol to evaporate from them more quickly than surrounding components.

High concentrations of alcohol can discolour some plastics or make them cloudy in rare cases, but I have never had an issue with this when wiping down the contacts of a 3DS cartridge.