st3 speedo

The speedo on my ST3 ( non ABS ) has stopped working. The orange (system fault) light EOBD is on . Otherwise it runs fine in fact this happened in Germany after several days of rain.So I have done 600 miles without problem to get home.
When I got home I put the printed circuit board on a warm radiator thinking water may have got in to it.But it still won’t work. All the rest of the display is fine ( except the odometer of course ).I can see no break in the wiring.
Where does the speed input come from ? There is a sensor on the back wheel but it doesn’t seem to have anything to trigger it .The workshop manual ,I have one a disc,doesn’t mention the sensor nor can I find it on the wiring diagram.
Can anyone help please ? If it needs a specialist to repair the printed circuit does anyone know of a good firm please.
As usual thanks in advance for any suggestions Philip Boobyer

I think the speedo sensor is number 29 on the wiring diagram.
The wiring diagram is in the back of the workshop manual, which you an download from Ducati under Dealers and Service/Maintenance.
It looks like a 3 wire sensor not sure what this picks up on though?

Kevin, thanks for that. I see it now but still can’t see it in the w/shop manual. Anyway all has resolved itself ,on Tuesday I spent hours going all over it again drying out anything I could,although nothing looked even damp, result late Tuesday, no change. I wanted to use the bike on Weds afternoon, amazingly everything is working fine again. A mystery.
I am told that the thing that look like a sender on the back wheel is just that and more likely to fail than the instrument . Apparently it is triggered by the bolt heads on the disc.A new printed circuit board is said to be £400 plus ? many thanks for your help Philip.

For info only— The speedo packed up again in December. After much messing about I replaced the speed sensor (£75) All now seems OK