Converting from +ve to -ve earth

iandec · Post by **iandec** » Tue Jul 12, 2011 12:02 pm

My Series lll OTS is undergoing a full restoration presently and would be grateful if somebody could advise me how to do the conversion.

Unfortunately it will not be ready for the E50 celebrations at Silverstone. :(

christopher storey · Post by **christopher storey** » Tue Jul 12, 2011 1:50 pm

Your S3 will be negative earth already. The change from positive to negative earth occurred when alternators replaced dynamos. In the case of the E, this was on the introduction of the 4.2 engine in 1964

iandec · Post by **iandec** » Tue Jul 12, 2011 2:03 pm

Christopher, Thanks for the information. My car is a 1974 USA model and the +ve is definitely connected to the chasis. During winter storage in Norway I disconnect and remove the battery, on re fitting, due to rushing I connected the poles the wrong way round and killed the Alternator. Silly mistake on my part. Are you still of the opinion that my car is negative earth? Cheers, Ian

PeterCrespin · Post by **PeterCrespin** » Tue Jul 12, 2011 2:40 pm

Christopher is quite right and I'm not even aware of ANY alternator car that is positive earth, though somebody will probably now cite a Mongolian earth-mover or something...

You may be getting confused by the fact that the power lead goes to a stud held to the body by a bracket. This may look at first sight like the earth stud, but the bolt is actually held in a nylon insulating collar and does not connect with the body in any way.

Alternatively, someone may have fitted incorrect battery leads so the negative one happens to be red or brown coloured and the positive one black. If so, they were mad, but you ought to check as it gets expensive otherwise.

Either way, the shop who sold you the alternator will confirm it was negative earth and the back of the alternator probably has a + symbol by the insulated output stud, which should obviously be connected to the positive side of your battery with the other side earthed.

Take care if you want to avoid further costly hazard.

Pete

christopher storey · Post by **christopher storey** » Tue Jul 12, 2011 6:16 pm

Unless your car has been modified in some bizarre way, you should find that the earth lead is the forward one of the two, and is bolted to the splashguard area of the car under or adjacent to the battery tray . The live terminal is the rearmost of the two, and goes to an insulated stud under the heater, with, as Peter says, a nylon collar interposed between the live stud and the frame bracket itself . Since you have had this mishap, it is perhaps worth dismantling the insulated post so as to satisfy yourself that this is indeed the live connection . The forward end of the stud should always be connected to the positive terminal of the battery , and the rearward end should be connected to two large brown wires which go through the sidewall of the footwell, copper nuts securing both of them

iandec · Post by **iandec** » Wed Jul 13, 2011 5:47 am

Christopher/Peter, Many thanks for the advice, it was much appreciated. Cheers, Ian :)

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Converting from +ve to -ve earth

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