Dyson only sell the complete head, they won’t sell the internal wiring or other parts to perform your own repair. You could try this link, a few recommended retailers that sell Dyson components. If not, try searching on Google.

How to: Order spare parts and accessories | Dyson Community

Dyson will only offer a replacement cleaner head, they don’t sell internal parts and don’t provide instructions on how to perform repairs yourself. You might have some luck on this link, the recommended retails sell some internal components. How to: Order spare parts and accessories | Dyson Community

If not, search on Google or visit YouTube, someone has probably done it themselves already. 

This video shows the process start to finish. 

You just need the wiring now. I suspect if you removed it and went to a hardware store, they’ll provide you with it. Must be standard electrical cabling. 

Thanks everyone. My husband can definitely do the repair, it was just finding the correct wire that was preventing it. I tried model railway wire which was too narrow. I've now bought some speaker wire that I'm hoping will be the correct gauge. Otherwise I'll try a hardware shop. Shame Dyson don't sell it. Not good for profits I guess but a whole new head seems such a waste of resources.