Replacement

Hi does anyone know we’re I could get a replacement  wiring loom/ harness please for gti 

Humm.. replacement best bet going to be eBay or  Crazyquiff's.
If you feeing up to it you can create them yourself if you have the old one and good manual for it.
All the connectors you can get from https://www.classic-vw.co.uk/ then the wire itself you can get from http://www.vehicle-wiring-products.eu/VWP-onlinestore/home/homepage.php.