I'm trying to work out if there's a fault with the speedometer in my Series III. I 've had the vehicle a few weeks and all seemed fine initially but while doing a long run from my old address to my new home in south Wales I noticed the readings seemed to be going crazy. At anything above very slow speed the needle swings around wildly and, even when it steadies, it seems to be reading way too high (eg. there's no way you'll convice me a fairly standard 2.25 petrol series 3 will do 80mph uphill into a headwind!).
Is this just yet another glorious Landrover quirk or is there something awry? If so what would be the prime suspects for the cause?
In case it's of relevence the vehicle is ex-military but has 12v electrics.