Speedo problem

When I got my car the speedo worked for a few days before it became intermittent but for the last month or more it has showed no sign of life at all. I had the right hand vent out and pulled the connector off the circuit board and the pins looked nice and clean so reconnected it but nothing changed.
I drove down to the hand car wash and still no movement but after the car/wheels had been jet washed the needle bounced erratically for quarter of a mile and then settled nicely give a fully working speedo. Now not working once more. So my question is, does it have a sensor/pickup or connector near the wheels that would have been disturbed with the jetwash?
Late GTA Atmo by the way.

Trevor

Sensor is on the box .There is a three wire multiplug from it down near the offside rear wheel though that could have been disturbed .

Also check the connectors in the drivers' side rear inside wing - behind the rear wheel. You'll see the lead coming from the gearbox that Lee mentioned leading to the connectors on the inside wing.
Have them apart, WD40 to shift any water then switch cleaner. That was/is often the source of a solution for my speedo, having sorted the dashboard end.

Jon