Right, first off the basic story of the Car.
1999 Renault Laguna DTi presented with overheating issue. If no electrical items are switched on the vehicle runs fine and the cooling fan cuts in at approx 3/4 up the gauge. If you then switch on electrical items such as Rear Screen heater, heater blower etc the temperature gauge rises up to virtually off the scale but live data says the car still isn't past approx 96 degrees and the fan still cuts in and out as it should.
Using my (lack of) knowledge I thought maybe a build up of potential on an earth, so thought i'd play with the scope.
If I did this right (waveform attached) then i indeed do have an earth fault. I connected the ChA reference to battery and the ChA signal to the block and then disabled starting (does that sound right?).
I appear to get approx 1v drop during cranking and that seems high to me?
All thought/comments/criticism welcome