Typical Wiring Diagrams for Negative earth Lightweight Alternators and Dynamo Look Alike Alternators

 

The main stud terminal is wired back to the battery and the spade terminal is wired back to your warning light. (The other side of the warning light is wired to an ignition switched supply, not earth.) The warning light must be 2.2 to 3 Watts and it must be wired in for the alternator to work.

Here are some typical installations when replacing a dynamo or multi-wire alternator. You should consult your cars wiring diagram and follow the simple rule above of main terminal is positive supply to the battery and spade terminal is warning light. Ensure your engine earth strap is in good condition or that the engine is otherwise well earthed and also ensure the alternator is well earthed through the bolts and mounting brackets. The wire from the alternator to the battery should be capable of taking 50 Amps (Voltage loss down the wire should be no more than 0.5 Volts).