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Battery Polarity change
Posted: Tue Jun 10, 2025 5:27 pm
by Derek Chambers
Hi all, I've decided to change the polarity on my 1961 Morris Minor and having checked out the procedure disconnected the battery and turned it around in the battery bay. I then reconnected the terminals to give me negative earth.
According to the information I've been given, I then disconnected the wire to the rear of the dynamo and shorted that connection to the live terminal of the battery and reversed the two connections on the coil.
On starting the car to check that all was working, the ignition light started blinking and even though the engine started and was running okay the ignition light staid on permanently.
Can anyone advise me as to what I've done wrong and how to overcome the problem Please.
Re: Battery Polarity change
Posted: Tue Jun 10, 2025 5:58 pm
by svenedin
There are TWO connections to the dynamo, F and D. F (field) is the connection to the field coils. D (dynamo) connects to the armature (via brushes) and is the output. To flash a dynamo, disconnect both cables from the dynamo and then connect a lead to the unearthed battery terminal and brush the other end of the lead to F terminal on the dynamo two or three times. F is the smaller of the two terminals on the dynamo.
Incidentally, if you simply turn the battery around you potentially have a dangerous situation of the battery terminals being at the front and at risk of shorting on the battery restraining bar. You should really get a new battery so that the terminals have the correct layout and are at the back.
Stephen
See this link for info on flashing a dynamo:
https://www.dynamoregulatorconversions. ... dynamo.php
Re: Battery Polarity change
Posted: Tue Jun 10, 2025 6:43 pm
by les
Regarding turning the battery, some have a small rim just below the battery top, if utilised, the restraining bar is well clear of the terminals.
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Re: Battery Polarity change
Posted: Wed Jun 11, 2025 9:35 pm
by Bill_qaz
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some batteries have the posts in a more centralised so no problem. with orientation.
Re: Battery Polarity change
Posted: Wed Jun 11, 2025 10:01 pm
by svenedin
I did say "potentially". Some batteries can be turned around safely but many cannot.
Stephen
This one on my car would not be safe turned around
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Re: Battery Polarity change
Posted: Thu Jun 12, 2025 8:49 am
by simmitc
Another option is to move the earth cable to the other side of the battery box and fit a longer cable to the other terminal. This does depend on having the correct style/size of clamp; butr leaves the original battery the same way round.