'06 DX Cab Chassis - GU2

Works fine on smooth roads, but has started working intermittently when on corrugated roads. Rev counter is fine, but ODO & trip counters may cease to count whilst the speedo is not working. I'm assuming a dodgy speedo cable or a wiring connection come loose. Can anyone suggest where I should start to look?

We are camped approx 90 minutes north of Broome with no phone reception so will have to wait until our next visit to town to catch your replies.

Thanks in advance,

Cuppa