Last weekend went out for longest run in J15 since building it. Went to watch Historic racing in Angouleme in France, really great trip. Very long way in a kit car!
Only had a couple of minor problems with car. It must have been charging but on a few occasions the starter wouldnt turn the motor over. It only seemed to happen when hot. My guess is the starter motor doesnt like beeing too hot.
Main problem was temp gauge. On the way back decided to show over 120 Degrees. The motor clearly wasnt that hot so suspect sender or gauge. Gauges are Caerbont (Smiths) and the single wire sender was a bit of a problem as I couldnt earth it very well so may have been the problem.
I'd like to replace it with a compatible sender with two wires to elimnate that as the problem.
Does anyone know of such a beast. My part number is TT3001-8N which I think is the 1/8 NPT.

the usual reason for senders not earthing well is: people using ptfe tape round the treads, also check engine earth straps.

Agreed, what make you think it is not earthed very well? What resistance value does the body of the sensor to engine give?

Its not earthed well because it is mounted into the plastic housing at the end of a Duratec cylinder head.
I had to screw it onto on of the electrical connectors thats like a washer (for want of a better description!).
i cant get an accurate resistance reading but putting the meter onto continuity proves that it is the problem.
A two wire sender is whats required.