The 'E' Type Forum

Are there any advantages to converting from Positive earth to Negative earth and as a rough guide, what parts would need exchanging on the car?

See similar topic below.....Steve

Hi Steve, I had already read through that one, more of a 'advantages' sort of question, we just realized that we have put a neg earth radio in! ha ha, luckily, no battery has been connected thus far so that's the only advantage I could think of which seems a lot of trouble to go through when we could just buy a pos earth radio.

You can get a radio polarity convertor.....Steve

Or buy a polarity converter to connect between feed and radio. I used one to allow my neg earth hidden Bluetooth receiver/amp to work in my pos earth car.

Just as an update, all S1 4.2's were/are Negative Earth so problem solved!

Apparently, the change was made in 63/64 with the introduction of the 4.2 engine with alternator? fitted from the 3.8 engine with dynamo/generator? fitted from factory.

Information from a very reliable source and standing by for incoming.

Sounds right, my Feb64 3.8 has positive earth. On mine a previous owner has fitted a 123 distributor and alternator - do these need to be replaced when converting from Pos to Neg earth?

Too technical for me to answer that one Darryl, I'll sloping shoulder that and let someone with more knowledge answer for you.

Darryl......123,s are polarity contiouse......u get pos and neg ones.....however u have an alternatof so sounds like previous owner may have converted it to neg eth.....just look at your battery connections....or test with a meter...Steve

I checked again Steve and the earth lead to the body is definitely from the positive battery terminal. Presumably the alternator is specific to positive earth

When I swapped out my dynamo for a powerlite Dynalite, I had to specify +ve earth configuration, same for my 1-2-3.

Javelin wrote: ↑

Tue Oct 26, 2021 3:17 pm

Are there any advantages to converting from Positive earth to Negative earth and as a rough guide, what parts would need exchanging on the car?

• You gain a small advantage in less corrosion of the bodywork

• You can fit any modern electronic accessory without problems

As for parts you need to exchange on a car that is still as it left the factory as a +ve earth car then the answer is the coil - and even that's optional but if you leave the original on you'll get a reduced sized spark.

In addition you need to change the wiring polarity to the in-tank fuel pump and flash the dynamo field winding over for -ve earth so it comes up and charges correctly. Likewise reverse the connections to the ammeter or it'll read discharge on charging.

Alternators are almost universally -ve earth and certainly as fitted by Jaguar when they moved over to using them.

Evidently the old pos earth clock won't work if you switch to neg earth.

This aricle from our Knowledge Base explains everything you need to know.
Positive to negative earth conversion guide: https://www.jcna.com/positive-negative- ... nversion-0

Having discovered I’ve got an almost new +ve earth Dynalite alternator and 123 distributor I don’t think it’s cost effective for me to switch to -ve earth. Shame. In all other respects it looks a fairly simple job.

As mentioned earlier in the thread. Until the twenties british cars tended to be negative earth. It was noticed that corrosion built up on the positive battery terminal causing loss of conductivity. The response was to change to positive earth, however after some 30 years it was observed that the corrosion occurred on the main body of the car. This was less acceptable so manufacturers reverted to negative earth. The advent of transistors re-enforced this choice of polarity.

So would it be prudent to disconnect the positive earth cable when the car isn’t being frequently used, to reduce the impact of body corrosion ?