my 59 has a 2 speed wiper but the washer doesn't work , I just bought a NOS washer bottle kit with pump but the install instructions refer to the single speed wiper, can I utilise the existing wiring without replacing the harness??

No,,,,,,,,,,,,The two speed wiper with washer was a factory option - came built in and in place of the standard single speed motor and no washer.The set up you have is an accessory washer to add to the exsisting single speed motor,etc....The factory two speed came with a washer as part of the option.Wiring harness and switch was different.There were three different switchs in 1959-single with out whaser,single with washer and two speed with washer and they all used different wiring and connections.