You might want to speak to Caerbont gauges about whether the Caterham speedo can accept a wheel speed sensor input. The pin out implies that it can, but I've never actually checked with them - and I would be interested in the answer! The Caterham speedo also has very limited calibration, so even if it can electrically, you might beed Caerbont to recalibrate it which is going to cost you £80. To put it back as Caterham intended, you'll need gearbox drive gear in gearbox, and not capped. Top hat and speedo drive connected to gearbox drive gear. Speedo drive connected to loom. Other end of loom connected to speedo. Speedo working.....