for some reason when my ignitions off my oil pressure gauge works (well it reads 5psi, sometimes 4 or 6. But when i turn the ignition on it goes to 0 and doesnt read anything when started. Also the same for my aftermarket water temp gauge. Nothing when running but when i switch it off it starts reading, i can watch it cool down. Any help is greatly appreciated!

Does your gauge have display something before or have you just installed them ?

Look like your negativ wire is a "positiv after ignition" ?

test if you have +12V on the neg wire you use with ignition ON and OFF.