748 Ducati 748 Erratic Temperature Gauge

Probably the thermistor. It may be breaking down and the resistance changes with the vibrations. It's this one.
https://www.ebay.co.uk/itm/36419262...amhx4rcrvk&var=&widget_ver=artemis&media=COPY
Situated on the left of the horizontal cylinder/coolant block.
Either that or perhaps a dodgy earth connection.

 

What if the temp gauge isn't working at all. Could it still be a dodgy earth or thermistor?

 

I had exactly the same thing happen to my 916 recently and it was cured simply by cleaning and tightening the grip (squeezing with pliers) the cable connector on the temp sensor, with any luck yours could be the same

 

Definitely, try the wire from the thermistor directly to ground. Gauge needle should then go all the way to the right. You can check the thermistor with heat, I can't remember the exact values but the resistance from the top connector pin to the body or ground on the bike should decrease with rising temperature. It's probably something like 750 Ohm at room temperature and going down when getting hot.

 

Connection to the temp sensor or reg/rec failing.

 

If you need a new temp sensor. Mk1 & 2 golfs use the same one

 

Had a similar issue. Try cleaning all the contact points on the sensors ie all threads and contact surfaces/sensor to alloy.

 

so likely electrical rather than a temp sensor itself failing?

 

my mate doesnt really know where the termistor wire is so where do i point him to?

 

It's connected where I circled in red.

 

ok thanks thats kinda what i told me dim mate already

 

The sensors can fail. The wiring connector is fairly common. The reg/rec can also cause it and we all know how reliable they were

 

I've used Electrex ones for years without too many issues. UK based so the back up is there if you need it.