Hi Carel,
All I can do is relate my own experience with the speedo sensors.A Guilietta sensor connected to a GTV or GTV6 box causes the speedo to overread massively.We are not even talking a small margin of error here,you will think the speedo belonged in a Mclaren F1...while the rev counter has barely moved!
The GTV or GTV6 sensor undereads equally badly connected to a Guilietta box,with a Guilietta speedometer.
Your solution would entail getting your speedometer changed for an electronic one,which I might have one spare at my folks place,with a GTV sensor in the box.Problem is they are very difficult to find last time I tried.
Fernando
P.S The next Track Day at Zwartkops is scheduled for March 13 and hopefully this time it won't be raining!
![Sad :(](./images/smilies/icon_sad.gif)