Page 1 of 1
polarity change
Posted: Tue Sep 05, 2017 10:50 pm
by mr.bird
hello all,has any one done the polarity change themselves,there seems to be much disagreement on the subject'
Re: polarity change
Posted: Tue Sep 05, 2017 11:33 pm
by palacebear
Straightforward polarity change should be easy enough as long as you aren't making any other changes. However, I can see little value in changing polarity for the sake of it. If you intend fitting accessories such as a cd player that demand negative earth then its a neccessity, as it will be if you convert to alternator charging in place of dynamo.
It used to be said that positive earth cars corrode faster than negative earth but I don't think there's much evidence to support that claim!
Re: polarity change
Posted: Wed Sep 06, 2017 10:31 am
by StillGotMy1stCar
First check that it has points ignition as it will fry an electronic one. The same with the fuel pump, check it has points and no small black cylindrical device with red and black wires if it has just reverse the connections, will most likely have nothing or a capacitor which can be connected either way. You will also need to change the battery terminals as the pos and neg are different sizes.
Disconnect the battery turn it round, just connect the neg terminal (the new earth), pull the small F wire off the dynamo and with a new length of wire connected to the F terminal of the dynamo flash it to the empty pos terminal of the battery a couple of times, don't hold it on for more than a couple seconds. This has your dynamo repolarised and you can reconnect the original wire back to the F terminal.
The next thing needed is the reversal of the coil terminals.
Job done.
I only changed my earth so I could fit a newer radio.
Regards John.
Re: polarity change
Posted: Wed Sep 06, 2017 4:36 pm
by geoberni
If in any doubt there are videos on the subject on youtube.
Re: polarity change
Posted: Wed Sep 06, 2017 6:45 pm
by SteveClem
Took me 15 minutes on a bog standard car, following instructions. If I can do it anyone can.
Re: polarity change
Posted: Wed Sep 06, 2017 6:58 pm
by StillGotMy1stCar
I have to admit I didn't bother changing the battery terminals, they aren't the best fit though.
Regards John.
Re: polarity change
Posted: Fri Jul 14, 2023 9:01 pm
by MorganP01
StillGotMy1stCar wrote: ↑Wed Sep 06, 2017 10:31 am
First check that it has points ignition as it will fry an electronic one. The same with the fuel pump, check it has points and no small black cylindrical device with red and black wires if it has just reverse the connections, will most likely have nothing or a capacitor which can be connected either way. You will also need to
change the battery terminals as the pos and neg are different sizes.
Disconnect the battery turn it round, just connect the neg terminal (the new
earth), pull the small F wire off the dynamo and with a new length of wire connected to the F terminal of the dynamo flash it to the empty pos terminal of the battery a couple of times, don't hold it on for more than a couple seconds. This has your dynamo repolarised and you can reconnect the original wire back to the F terminal.
The next thing needed is the reversal of the coil terminals.
Job done.
I only changed my
earth so I could fit a newer radio.
Regards John.
Sorry to revive a dead thread, just wondering if where it says
"The same with the fuel pump, check it has points and no small black cylindrical device with red and black wires if it has just reverse the connections"
It means you only really need to reverse them if it's not on original points system?
Re: polarity change
Posted: Fri Jul 14, 2023 9:12 pm
by svenedin
MorganP01 wrote: ↑Fri Jul 14, 2023 9:01 pm
StillGotMy1stCar wrote: ↑Wed Sep 06, 2017 10:31 am
First check that it has points ignition as it will fry an electronic one. The same with the fuel pump, check it has points and no small black cylindrical device with red and black wires if it has just reverse the connections, will most likely have nothing or a capacitor which can be connected either way. You will also need to
change the battery terminals as the pos and neg are different sizes.
Disconnect the battery turn it round, just connect the neg terminal (the new
earth), pull the small F wire off the dynamo and with a new length of wire connected to the F terminal of the dynamo flash it to the empty pos terminal of the battery a couple of times, don't hold it on for more than a couple seconds. This has your dynamo repolarised and you can reconnect the original wire back to the F terminal.
The next thing needed is the reversal of the coil terminals.
Job done.
I only changed my
earth so I could fit a newer radio.
Regards John.
Sorry to revive a dead thread, just wondering if where it says
"The same with the fuel pump, check it has points and no small black cylindrical device with red and black wires if it has just reverse the connections"
It means you only really need to reverse them if it's not on original points system?
If you have an electronic SU fuel pump they are only one polarity. They will not work if the polarity is changed. The only definitive way to tell is to remove the cap from the pump and look. The
positive earth electronic pump should be marked with a red band of tape. The negative
earth version has a black band.
The modern points pump will work either polarity BUT some old points pumps were fitted with a diode across the points which means they need the connections switched round and they will then function normally. The best way would be to reverse the diode in the pump in these circumstances (or remove it but this will lead to more arcing at the points). The modern points pumps have a Zener diode that works either way round.
It is possible to switch out the circuit board in an electronic pump to the other polarity. A kit is about £85 from SU. It is a DIY job with care.
Stephen
This is a
positive earth (red band) electronic pump
- IMG_9470.jpeg (913.57 KiB) Viewed 901 times
- IMG_9471.jpeg (2.06 MiB) Viewed 901 times