1997 Peugeot 806 diesel - Speedo not working - Boggy

brother in law had new clutch fitted recently, works fine but speedo has ceased to function - the garage concerned will apparently 'consult a Peugeot dealer' to find out why, but frankly it needs fixing - is there a simple diagnostic / part from scrapyard? Does a cable just screw into the gearbox that was not reconnected and could we do it ourselves? any help / advice appreciated as always.

1997 Peugeot 806 diesel - Speedo not working - Peter.N.

if this uses a 1.9 XUD engine there is a sensor mounted on the diff housing just above where the o/s driveshaft fits in which could be the problem, it maybe that they didn't plug it back in. if the sensor is faulty its not difficult to change.