This is a tricky question cause different pickups have
different schemes.Seymore Humb.Green=Hot,Dimarz.Red=Hot
Lawrence Black=Hot.In most cases black wires are ground
wires.Solder this to the tone pot.Try touching the others to the pickup select switch.Use a screw driver
for testing(tap it on p.u.).The if there is buzzing, then pickup is in single coil mode.It’s really trial and error,if there’s no guide sheet with pickup.