Classic cars forum & vehicle restoration.

[Ray White]

Whilst I think I understand what happens with reversed polarity I and how to flash the dynamo to rectify it, I am not at all clear about how I should rectify the problem when the car has electronic ignition.

I am just concerned that terminal damage may be caused to the (expensive) new electronic distributor should the polarity get reversed. For all I know; it may not even be relevant if an alternator is fitted.

I am hoping someone will be able to give me some practical advice ...?

[ukdave2002]

Ray, I thought you had an alternator rather than a dynamo? If so no need to flash it. If you do have a dynamo flash it off the car to protect any potential damage to electronics.

I doubt reverse polarity would damage the electronics, but flashing a dynamo certainly might.

Dave

[Ray White]

[ukdave2002]

[Ray White]

[petelang]

Ray, your battery terminals are different sizes in order to prevent it being incorrectly connected.
Nowadays, most electronic stuff is made with reverse polarity protection, so I would envisage this is the case with the electronic distributor. However the alternator/dynamator will probably not be so protected and reverse polarity would short circuit the battery supply straight through the 9 diodes in the AC to DC rectifier pack and it will be toast!
The same would be the case with any diodes inside relays, instruments and those you put in the dash, probably also take out the flasher unit.
So to sum up, make sure your battery terminals are correct size and well marked and put a big sticker on the battery as a reminder if ever jump starting that it's is POSITIVE EARTH.
_________________
Daimler Fifteen 1934
Armstrong Siddeley 15 Long 1933
Daimler V8 250 1969

[V8 Nutter]

I know some one who only recently fitted a battery the wrong way round on a 1970's Buick, should have been negative earth. The car started no problem, but it destroyed the alternator. Everything else survived.

[ukdave2002]

[Ray White]

I am pretty much dialled into the MG TC being positive earth and there is no chance of the battery being joined up the wrong way round - as has been said - the cables (which, by the way, are all new) have different size terminals.

My dear old Swallow, on the other hand, hasn't seen much use lately and if the battery has died and the dynamo should happen to have lost it's inherent magnetism, I believe there is a risk that it may have got it's polarity a bit confused (note technical terms).

it is negative earth and proud of it.!

The Swallow remains unmolested and will continue to hold the fort with regard to originality.

[MVPeters]

Ray
Re-polarising a dynamo isn't anything that needs to be done on any kind of regular basis. It takes years for them to get confused.
Hopefully, you can run the Swallow once in a while.
You do need to be cautious around alternators, however. Sparks & shorts & sudden high-current draws can be hazardous to their welfare. Disconnect it before any welding, for example - it may not be essential, but better safe....
_________________
Mike - MVPeters at comcast.net
2002 MINI Cooper 'S'

[Ray White]

Thank you Mike. Your advice is always appreciated.