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MG MGB Technical - Bosch Alternator Question

I mounted a new Bosch alternator in place of the old generator in my 1965. The ignition light will not go out. The small wire should go on one of the two leads on the alternator? Which one? Does anybody know?
Frank Baker

A 65 would have been pos earth dynamo with separate regulator Frank. I don't know what set-up you are now moving from (ie whether it has been already coverted to neg earth and/or alternator) but this link may help,

It is negitive ground
Frank Baker

There loads of variations and many cars have been modded by now.
1) Are you changing the polarity now to neg or has it already been done and working properly before?
2) Does it still have the external regulator on the RH inner wing connected?
3) Are you fitting the Bosch alternator in place of another alternator (if so which) or a dynamo?

In converting a dynamo/generator to alternator as Frank says there is more to it than connecting the two dynamo wires to two spades at the alternator, as this keeps the original control box in circuit and I wouldn't like to say what the effects of that would be.

The simplest way of converting from dynamo to alternator is:

1. Disconnect the battery ground strap.

2. Remove the two brown/yellows from the control box, connect them together, and insulate them from coming into contact with anything else.

3. Connect the brown/yellow at the alternator to the indicator terminal, which may be marked IND, or be smaller (standard sized) than the other one or two output terminals.

4. Connect a new heavy gauge brown from the output terminal(s) of the alternator to the battery cable stud of the solenoid.

5. Tape back and insulate the original brown/green that went to the F terminal of the dynamo.

6. Reconnect the battery ground strap.

If you remove the control box altogether you will have to connect together and insulate from everything else the three brown wires that terminate on it. The remaining brown/green and black wires from the control box should be taped back out of harms way.

If changing *polarity* at the same time (Frank indicates his has already been changed) you would have to consider whether you have an electronic or diode quenched fuel pump and make appropriate changes, reverse the polarity of the 12v and ground wires inside the tach, reverse the heater blower wires (check which gives best blow), and possibly slightly adjust the position of the wiper arms on the spindles. Any after-market electronic stuff is extra.

Paul Hunt

Check out the links on this site, . There are many discussions about wiring these up and hopefully there will be the key info you are looking for here.
Bob Muenchausen

This thread was discussed between 27/02/2005 and 03/03/2005

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