Classic cars forum & vehicle restoration.

[Albioninoz]

I have a 1958 Rover P4 105S which is still positive earth. I am confused as to the practicalities of this. I want to instal an electric windscreen washer pump but am unsure what the remifications are regarding wiring it up. Do I just wire it up in the normal way or do I have to make sure that the positive terminal goes to earth? Any help would be appreciated. Thanks, Ray

[roverdriver]

This question comes up from time to time on the Rover P4 Drivers Guild of Australia website and forum.

Basically any accessory that has an insulated body, and therefore two wires to power it can be used with + earth or - earth. Beware of wireless sets (radios) because the aerial is usually 'earthed' and therefore can cause a short circuit with disastrous consequences.

It is so easy to change polarity, the first time was an unintended 'swap'. I simply put a new battery in and connected negative to earth in error. The engine started and behaved as normal, but the ammeter read backwards. In realising what I had done, I simply swapped the wires over on the meter and voila! I had a negative to earth P4. Subsequently I have done several Rovers the same way without any trouble.

While the OCCC Forum is a great source of information,(and always an enjoyable read!), I would strongly recommend joining the Aussie Rover P4 Guild which is based in Melbourne. P.M. to me and I can give you a link and details.

Good luck and happy Rovering, Dane.
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Dane- roverdriver but not a Viking.

[ukdave2002]

Ray, as you suggest it seems odd to have a positive ground! most vehicles in the 30's were negative earth, then some research indicated that a positive earth would reduce corrosion, hence the change. The change back to negative ground took place in the 60's, the corrosion benefits were minimal and together with the increase of solid state electronics into vehicles there was presumably a commercial benefit.

Converting from positive earth to negative earth is quite simple; in addition to Danes points; small motors as found on things like your washer pump are probably permanent magnet so the connections will require reversing , larger motors like the starter are series wound so will be fine as they are. The coils LT connections should be swapped round and of course you will need to "flash" the dynamo to polarise its fixed magnets.

Dave

[consul 57]

i fitted a washer pump to my pos earth consul, all i did was reverse the wiring to it, i.e. fuse between motor and body, earth to the battery, works fine although i am going to go to neg earth soon.