If you change the polarity of the electrical system or fit a new dynamo then you need to polarise the field windings before connecting it to the regulator. The following is a question from Bob S and a reply from Norman Verona (corrected by Peter Cole) from the mg-tabc group on 2nd August 2016.
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My ignition light came on and the last time it did this all I had to do was to polarize the system, but I can't remember which posts your supposed to connect to polarize the charging system.
I'm sure somebody out there remembers and can help me out.
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Assuming you’re still positive earth, take a heavy wire from the negative battery post and “flash” it against the F terminal (smaller of the two) on the dynamo.
[Note that you take the wire from the unearthed battery terminal. So if you have a negative earth then you take it from the positive terminal.]
However, this only ever needs to be done once so I doubt it needs doing again.
If you make up a small lead with tags on both ends, remove the wires from the dynamo and fit the link wire between the two terminals. Then using an analogue voltmeter (digital is OK but much easier to see the output on an analogue), clip the black lead to one end of the link wire, the red to a good earth. Start the engine and slowly increase the revs. You should see the voltage rise. Don’t let it go over 20v. Assuming you do see 20v the dynamo is working so test the wiring. Put the wires back (remove link). Start engine and clip the black lead to the D terminal on the regulator (5th from rear). Start engine and ensure you still have an output. If you do then the regulator would seem to be faulty, if there is no output it would appear the wire is broken. The wire from the D terminal on the dynamo and the D terminal on the regulator should be yellow. Also make sure the wires on the regulator haven’t come out the terminal. Just gently pull a wire at a time down (there are two) and ensure they’re both still screwed in.
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Return to Notebook© David James 2016 Last updated: 2nd August 2016