Neg or Pos Earth


New Member

I am checking to see if my 1959 P4 75 would be negative earth or positive earth please. I do not have aceess to the car at the moment to check where the leads go to so any help appreciated


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It would have been positive earth when new, and looking at the leads in the picture, the negative is routed through the armoured conduit to the front of the car , it is still probably positive to the frame . I would double check just to make sure there are no modifications outside the scope of the picture.
I have seen conversions to neg earth work fine except for one issue - if the coil terminals are marked '-' and '+' they can be polarity sensitive - make sure these connections are correct polarity.
it would of been postive when new, but impossible to say now, in my experience most cars have been converted to negative earth
Is there any experience here of how much effort would be involved in converting a P4 from positive to negative ground? My P4 from 1958 is definitely positive ground.

Rover P4 75 1958 09.jpg
If it's still dynamo the only thing I can remember is to take the cover off the voltage regulator and keep an eye on the contacts on the bobbins because they can stick shut.
If its a dynamo it will work on either ground , ammeter will work back to front unless the terminals are reversed and as stated the coil low tension terminals will also need reversing . The dynamo may need " flashing " over by briefly closing the cut out contacts on the voltage regulator after reversing the battery terminals. If it has a radio that might be a problem ! Obviously if there are any electronic additions they would need to be looked at for polarity sensitivity .
all you need do is swap battery, wires on ammeter and reflash dynamo, no need to bugger around with control box, just flash field terminal to battery positve